The Library (Level)

Looking for the Library structure?

The Library begins after 343 Guilty Spark teleports the Master Chief from the swamp he was in (part of the previous level) into the Library of Installation 04. Equipped initially with a Pistol and an Assault Rifle (shotgun is primary for the second player in co-op), he must battle through four Flood-filled levels to reach the Index chamber. This is the first and only level where Sentinels will be your allies for most of the level. This is also the only level that you're not fighting against the Covenant foes.

It should also be noted that many players of the Halo series consider this to be one of the worst levels in the Halo series. They feel that the hallways are nearly identical and you fight waves and waves of similar enemies. The map's layout is confusing, and it is difficult to stay alive. Because of this, Bungie made the Library much shorter in Quarantine Zone.

Usable Weapons

 * Pistol
 * Assault Rifle
 * Rocket Launcher
 * Shotgun
 * Frag Grenade
 * Plasma Pistol
 * Plasma Rifle
 * Needler
 * Plasma Grenade

Part 01: The Library
(Opening cinematic-flythrough of the main central chamber of the installation, through a bizarre rotating doorway, to find 343 Guilty Spark and the Master Chief teleporting in)

343 Guilty Spark: We must collect the Index before we can activate the installation.

(Over the course of the level, 343 Guilty Spark mutters all sorts of random phrases. Here are most, if not all of them)


 * Huaaaaa, huaaaauuuuhummmmm.
 * Ahhhh...I, am a genius. Heeheeheehee!
 * Ah.
 * Oh. Hello.
 * Hadaadeeeeiiiii, hadadummm.
 * Hmmmhummmm, hahummmhmmm. Hmmmhu-umhaummmm.
 * Hahahahaha!
 * Laaaa, dadadadadaaaauuuuhhh.
 * Oh, that's a good idea! (When you reach one of the rotating doors)
 * Reclaimer, we must keep moving! ...Reclaimer? (If you die)
 * Hmm, unfortunate (If you die)

343 Guilty Spark: We are near the Index chamber. Follow me.

(When you emerge into the large central chamber)

343 Guilty Spark: The energy field above us contains the Index. We must get up there.

(When you come to a huge door, which is locked)

343 Guilty Spark: The security doors have sealed automatically. I will go access the override to open them.

(When Spark returns)

343 Guilty Spark: Please, follow closely. This portal is the first of ten.

(If you go the wrong way)

343 Guilty Spark: That is not the correct direction, Reclaimer. If you do not follow me, you may become lost.

(As you move into the next hallway)

343 Guilty Spark: Puzzling. You brought such ineffective weapons to combat the Flood, despite the containment protocols.

(Moving down another hallway)

343 Guilty Spark: The Flood must not escape the installation. They would consume all.

(Another hallway)

343 Guilty Spark: You can see how the body's been transformed by the genetic restructuring of the Flood infection. The small creatures carry spores that cause a host to mutate. The mutated host then produces spores that can pass the Flood to others. It is insidious and elegant. As long as any hosts remain, the Flood is virulent.

(Going down yet another hallway)

343 Guilty Spark: We must continue. This way please.

(Further down the same hallway, just before you're jumped for the first time from all sides)

343 Guilty Spark: This installation's research facilities are most impressive! Perhaps we'll have time to see them later.

(As Spark sends a squad of Sentinels to assist you)

343 Guilty Spark: These Sentinels will supplement your combat system. But, I suggest you upgrade to at least a Class Twelve combat skin. Your current model only scans as a Class Two, which is ill suited for this kind of work.

(As you near the first platform lift)

343 Guilty Spark: Pardon me. A plasma conduit breach in section 5-5-2-4 has disrupted power flow to a gravitic maintenance assembly. Repairs require my attention. I will return soon.

(As you ride the first lift)

Part 02: Wait, It Gets Worse!
(A little bit down the first hall of the second floor)

343 Guilty Spark: Flood activity has caused a failure in a drone control subsystem. I must reset the backup unit. Please, continue on. I will rejoin you when I have completed my task.

(Another hallway)

343 Guilty Spark: The Sentinels can use their weapons to manage the Flood only for a short time. Speed is of the essence.

(Another locked door)

343 Guilty Spark: Please wait here.

(Hallway)

343 Guilty Spark: Your environment suit should serve you well when the Flood begins to alter the atmosphere. You are a good planner.

(Hallway)

343 Guilty Spark: The installation was well conceived. It is surely the only way to end the Flood threat.

(As you ride the second platform lift)

Part 03: But I Don't Want To Ride The Elevator!
(Hallway)

343 Guilty Spark: I would conjecture that the other species currently on the installation is responsible for releasing the Flood. They seem most persistent in their attempts to access restricted areas.

(In a large, open, cavernous hallway)

343 Guilty Spark: Why naturally the Flood is simply too dangerous to release, and mass sterilization protocols may again need to be enacted. Of course, samples were kept here after the last catastrophic outbreak...for study. It seems... that decision may have been an error.

(Another hallway)

343 Guilty Spark: The installation was specifically built to study and contain the Flood. Their survival as a race was dependent upon it. I am grateful to see that some of them survived to reproduce.

(Coming to ANOTHER locked door)

343 Guilty Spark: I will deactivate the security lock. Wait here.

(ANOTHER hallway)

343 Guilty Spark: Please stay close. Time is short.

(ANOTHER platform lift)

Part 04: Fourth Floor: Tools, Guns, Keys To Super Weapons
(Hallway)

343 Guilty Spark: The Flood are already hard at work repairing your vessel. Its parasitic nature belies the Flood's intelligence.

(Final cinematic, when you cross a small bridge onto a bizarre, cluttered platform which quickly begins to descend)

343 Guilty Spark: The energy barrier surrounding the Index will deactivate when we reach the ground floor.

(When the platform comes to a stop)

343 Guilty Spark: You may now retrieve the Index.

(The Chief walks slowly over to the Index, which is held in a sheath of some sort. Sections of the sheath move in and out for a few moments, before the Index itself pops slightly out of the top of the sheath. The Chief removes it and stares at it for a moment, before 343 Guilty Spark zaps it from the Chief's hands and into some sort of trans-dimensional pocket)

343 Guilty Spark: Protocol requires that I take possession of the Index for transport. Your organic form renders you vulnerable to infection. The Index must not fall into the hands of the Flood, before we reach the Control Room and activate the installation.

(Spark and the Master Chief teleport away from the platform)

343 Guilty Spark: The Flood is spreading! We must hurry!

Walkthroughs
Writing a walkthrough for the Library is much like writing a manual for wiping out an anthill with your bare hands while covered in honey; you can plan, script and describe all you want, but when you’re in the middle of a fight, anything can and will happen – and you can't plan for every possible outcome. In this Library, you won’t find any books. What you will find, however, are seemingly endless waves of Flood bent on making you a statistic. Your goal for this level is to follow the Monitor around the spiraling floor plan up to the index access point. The index serves as a key to activate Halo’s defense systems and destroy the Flood.The ideal weapon is the shotgun.

Part 01: The Library
You will teleport to a somewhat safe location at the back end of a large room. As the Monitor moves forward, follow him with extreme caution. As you pass the first outcropping on your left, you’ll notice a puffy, inflated Flood form shaking violently like a living castanet stuffed with Mexican jumping beans. Enter the Flood carrier: an impregnated Flood form that spreads its seed by detonating. Whip out your pistol and concentrate your fire on the carrier. When he pops, any infection forms surrounding him will follow suit and likewise explode. Quickly pull out your assault rifle and spray the ground with bullets to take out any remaining spores. Looking ahead, four carriers will begin charging your position. Swap back to your pistol and take out the frontmost carrier. Popping the carrier in the front will cause an explosion that will send the other carriers flying from the point of detonation. Killing a carrier at the rear of the pack will send the rest flying towards you. That would be bad. The thing to keep in mind when fighting the Flood is to always concentrate your fire on a carrier when other forms are near him. As in the Myth games, where seasoned players jump at the chance to take out a Wight in a cluster of troops, you can damage several enemies at once without using much ammo. If your energy level is adequate, you can allow the remaining spores to burst on your shields, or just melee attack them. Follow the Monitor forward cautiously until you see red blips appear on your motion tracker again. Immediately backpedal to avoid getting flanked on both sides. Using your pistol, take out any immediate threats first, concentrating on the carriers. After that wave, turn on your flashlight, scan the floor for ammo and move forward with caution. The moment you find a shotgun, swap it for your rifle. At the end of the room, a couple of carriers will be standing still. Use your pistol to pop them and back up right away. A group of well-armed Flood will charge from the outcroppings ahead. Toss a frag grenade just in front of them. Keep your pistol trained on them and don’t let yourself get surrounded. Pummel away and creep forward when the fighting stops. Another small wave may come forward; repeat the procedure until the room clears and you checkpoint. Allow your shields to recharge and follow the Monitor out the doorway to the right. You will enter the vast central room of the Library. Quickly turn to your left and take out the armed Flood Fighters to your left. Immediately whip around and open fire on the Fighters to your right. Often the Flood carriers will try to surprise you by hiding in a nice ambush spot. When you are preoccupied in battle, they will emerge. Try to take them out at a distance with your pistol before they go back into hiding. Keep a close eye on your shields. If you have to, run back into the doorway to avoid being surrounded by Flood spores while your shields recharge. Once all the large forms are gone (infection forms will keep appearing sporadically) follow the Monitor to the doorway on the left.

Once you walk into the entry hall to the next room, a group of Flood will literally come flying toward you. The second you see a Flood fighter jump from behind the unit ahead, throw a plasma grenade on the floor in front of you and back up. As soon as it goes off, toss another one in the doorway. Several more Fighters will appear and fly forward from the explosion. If any survive, mop them up with the shotgun. If you accidentally tag a fighter with a plasma grenade, blast him with your shotgun to stun him long enough for the grenade to go off; if he charges you, all bets are off. Step into the next room. Your presence will trigger a few small groups of Flood to jump from two ducts directly ahead. Back up into the central room and use grenades and the shotgun to clear them out, using the entryway as a choke point. Repeat this procedure until the ducts stop spewing Flood.

When you emerge into the next room, you’ll find it very similar to the first one you were in. Pull your pistol out and take out as many enemies as you can from a distance. Use a grenade or two. If you start to get swarmed, back up to the entry hall again, forcing the Flood into a single file line as you blast away at them. Watch your shields. If they gets low, back out and run around to avoid spores until your shields recharge. When the Fighters stop coming, go back in the room and scrounge around the floor for goodies. Switch to your pistol and move forward. When you reach the Monitor, a fighter on the outcropping to your right will open fire on you. Snipe him with your pistol before he gets a chance. Stand under the Monitor and wait for the large set of doors to open. Move through the doorway into the next room.

There is nothing but a cluster of spore forms waiting to the left, so take a right into the spacious hallway. On the floor ahead there will be three glass panes. Inevitably, the carriers will swarm the glass, shattering when they pop. Don’t forget about these three nasty holes, as you will be fighting around them soon. A group of Flood will appear around the glass. Shoot with your pistol and grenade them from a distance. Switch to shotgun when they get close. Always look for cover. There’s going to be a lot of shooting going on, so you aren’t going to want to be out in the open. The last thing you want to do is charge ahead full bore. Trigger one small group, back up, destroy them. Repeat. Repeat. Repeat. If you run out of shotgun shells, swap your gun for an assault rifle. It’s better than plasma and definitely better than nothing. When the large hall comes to a “T”, you will go left. A small group will come for you. Use grenades and pistols from a distance, shotgun at close range. Duck and cover.

Follow the large hall around until you see Guilty Spark again. A small group of Flood will pour from the duct ahead. Use grenades and backpedal around the corner to take cover while shooting. Around the corner to the right will be a health pack. A slot in the floor will have a super shield. Be advised that as soon as you round the corner a group will jump from the slot. Toss a grenade in front of the short ramp and trigger the Fighters right before it explodes to watch them soar. A few more Flood Fighters will appear before you can pick up the overshield but they shouldn’t give you too much grief. When the coast is clear, go down the short ramp and pick up the powerup. Overshields are a lifesaver when fighting the Flood. Since they are scarcer than bullets, you will want to open fire on the spores rather than letting them whittle down your overshield. Moving forward, you will trigger an ambush that will approach from in front and behind. Immediately back up to avoid getting swarmed and open fire on the Flood carrier closest to you. Take cover and fire at the Fighters as they come. Concentrate your efforts on the Carriers. Scoot forward slowly. Blips will appear ahead by another group of three glass panes on the floor. You can pretty much take out that group from a distance with your pistol. Once the coast is clear, creep past the fresh holes in the floor until you come to another bend in the hall. Turn right. Ahead another group of Flood will appear. However, there are enough walking pus pouches that you shouldn’t have much trouble eliminating them. Take the jog to the right past the library’s AV department and keep moving forward. Another group of Flood will appear, but this time a group of Sentinels will come to join the fight. Don’t feel too obligated to save them since they won’t follow you up the nearby elevator. Give them a hand, neutralize the threat, scavenge around for ammo and hop on the massive elevator platform at the far end of the hallway.

Part 02: Wait, it gets worse!
Step off the elevator and head toward the doorway. To your right, a cluster of Carriers will drop. Blast them with your shotgun and step back to avoid their explosion. Head back in and go to the right. Sentinels will emerge from the alcove to your left. Move forward past the bank of 200” Jumbo-Tron screens and take the jog to the left. The Monitor will leave you and the sentinels to take out another small group of Carriers. Directly in front of you is another slot in the floor. This one has two health packs, so use one if you need it. Keep moving forward until you checkpoint. You will then get the infamous message: ”Hold your position until the Monitor returns.” Here’s where we have fun.

Go to the far end of the room next to another health pack on the floor. Toss a grenade into the nearest duct on your right. The Flood will begin pouring out of the ducts, so stay in that little alcove and let them come to you. Cream them with a little shotgun and ‘nade. When you get down to your last grenade, toss it in the middle of the room and run through to the opposite side of the room. You should pick up a few goodies along your way. Continue doing what you’ve been doing until the Monitor returns. Grab a health pack and follow him through the big doors.

This next room is the large circular room directly above the index. Whip out your pistol and follow 343 Guilty Spark. A large group of Flood will show up ahead. Toss grenades ahead of them and open fire on the Carriers behind. See how high you can make the Fighters fly. Repeat with the next group. Repeat with the third group, keeping an eye out for rockets. When the coast is clear, scan the floor for ammo. Resist the urge to pick up the rocket launcher; it will just mess you up due to the time it takes to line up a shot and switch back to a close range weapon. At the end of the room there will be another set of doors. You’ll also get another message to hold your position. Relax. This one’s easy. Go grab a rifle behind you and mop up the waves of spores as they come towards you. Shortly the Monitor will return and the doors will open. Clear away the popcorn forms, swap your weapon back and move through the doorway.

Follow 343GS to the right. Ahead will be another slot in the floor, but this time the descending ramp actually goes somewhere. Take out the small pocket of Flood resistance ahead and proceed down the narrow ramp. Pull out your pistol and pop the Carriers. Carefully peek around the corner ahead and pop the pregnant pusballs waiting for you there. Move forward down the narrow walkway until you see the exit. Several Flood forms will jump down. Back up and use the corner of the hall for cover. Toss grenades and use your pistol until the area is clear. Move up the ramp and out the exit. Spores will be there to hop down on you so make sure your shields are full. Follow the Monitor to the left. Stop right before the hall comes to a “T”. This AV corridor will have Flood attacking from both ends, so stay back and clear this hall like so many you have before. Once the waves of Flood dry up, move forward and follow the large hallway. When the Hall comes to a “T” again, pull out your pistol and turn right. At the far end will be a large group of Flood Carriers and a pair of rocket wielding Fighters. Stay back so you can dodge the rockets and start popping Carrier forms as fast as you can. When you've killed them all, move forward. A health pack will be in the corner to your left. If you need it, take it and follow the hall to the right. Another group will jump you. Fight them till they stop coming. If you feel compelled to pick up a rocket launcher, drop your pistol in a safe spot so you can pick it up immediately following this encounter. Follow the Monitor. An ambush will appear, but if you just keep moving forward to the elevator, you can avoid a fight altogether. Ride the elevator up.

Part 03: But I don’t want to ride the elevator!
Hop off the elevator and turn left. You’ll come across a group of Sentinels fighting the Flood. Help them out if you want. Sometimes the Sentinels do more harm than good, though. Head down the ramp in another slot in the floor ahead. Follow the narrow hallway around. When you get to the turn, pull out your pistol and snipe the small group ahead. A large group of Infection forms will show up. Send them away with your shotgun. Lastly, at the next bend will be two Carrier forms. Toss a grenade around the corner or carefully snipe them from a distance with your pistol. When you reach the exit, a group of Flood and Sentinels will appear on your motion tracker. Back up and let them duke it out. When the blips on your motion tracker stop, proceed up the ramp. The Flood will have won and there will be plenty of survivors. Head back down the ramp and use it as a choke point, letting the Flood funnel into your sights. When the area is clear, move up the ramp and into the room.

Turn right, pass the three consoles and turn right at the row of screens. Turn right again and follow the hall until it dead-ends. You’ll be asked to wait until the Monitor returns again, but this fight will be much easier than the first. There are just enough Carrier forms to make this a shotgun-only battle. There will be a health pack in the far corner when you are finished. Follow the Monitor through the doors when he returns. This will be the third floor of the index room. This time you’ll go clockwise around the perimeter. A group will initially attack from the left. Use your skillz and gunz to eliminate the threat and move on. The next group of Flood will drop onto the two tall blocks directly ahead. Stay back and use your pistol to snipe them before they can ream you. Move through the doorway into the next large, winding hallway.

A health kit will be sitting on the floor ahead, should you need it. Follow the Monitor to the right. Switch to plasma grenades ad pistol. Stick a plasma grenade to the floor in front of the slot ahead. Three Flood forms will jump from the slot right about the time your grenade goes off. Pop the other forms with the pistol as they come towards you. Switch to your shotgun if any get in close range. The hallway ahead will come to a “T”. If you go forward, you’ll trigger groups of Flood on both ends of the “T” so back up and take them out, triggering one group at a time like you’ve done before. Take a left, left, right, right to the next set of large doors. Squeeze through the opening into the next room. Trigger the checkpoint and it will tell you to stay here until the Monitor returns. Slide into the niche between the outcropping and the double-doors and reload your shotgun. Don’t go too far back - just far enough to use the outcropping as cover. You won’t be able to stay here for long. Fight the Flood as best you can with grenades and shotgun shells. When your health gets low, use the health pack in the center of this room. Always reload as soon as there is a momentary lull in the action. You’ll end up having to use plasma grenades to supplement your arsenal. Try to hit the ground as best as you can. If you start getting surrounded, move to the niche on the other end of the room, picking up grenades on your way.

Once the doors open, several Sentinels will come to your rescue. Go out the doors and follow the hall to the left. Hang back and help your Sentinels fight the next group of Flood by using your pistol at a distance. Follow the hallway around to the end where you will get to the elevator again. Beware kamikaze Carriers that will drop from the ceiling as you go by.

Part 04: Fourth Floor: Tools, Guns, Keys to Super Weapons.
As you get off the elevator, a few Flood Carriers will drop from above. Be watchful and get away if one gets next to you and prepares for self-detonation. There’s a health pack right here in case you need it. Follow the path to the adjacent bank of video screens where the hall comes to a “T”. Does this sound familiar? Go forward, trigger each wave and pull back to take cover behind an outcropping, letting the flood funnel to you at a trickle. Repeat this process again until they stop coming. Move down the hallway. You’ll eventually come to another slot in the floor with a ramp leading down to a small tunnel. Does this sound familiar? Head into the tunnel. Around the first bend will be a Carrier or two with a large swarm of infection forms. Pop them and proceed. There will be a couple more around the next bend. Pop them and proceed. If the Flood weren’t so much fun to blow away, this might actually get monotonous. Proceed forward up the ramp and take an immediate right. Although it doesn’t say so in your objectives, this will be another one of those “wait for the Monitor to return” moments. Stay in the niche on the right. If you go to the far left side, fighters will pour out of the opening above and on top of you. Besides, on the right there is a health pack available when you need it. There's another one on the other side of the door, so don’t feel obligated to save it for later. When the Monitor returns, move through the open doors and out. The health pack is in the floor slot ahead. Move forward; we’re almost there. Eventually, you’ll trigger the next wave of Flood. However, there won’t be an easy fall-back position. At this point, you need to just run and gun. Blast through the Flood quickly and get your butt out of there. Eventually you’ll come to a large pair of doors on your left. This is not a good place to turn and stand your ground. The Monitor will come and open them, allowing another wave to pour in from behind. Keep moving and duck in the first niche past the door. THIS is where you will make your stand. Use plenty of grenades and blow away anything that moves. When the coast is clear, move toward the open doors.

Ahead, you will see the central elevator that rides an energy beam down to the index. Although it may look clear, don’t be fooled. There is a massive flock of frikkin’ Flood waiting on the sides to flank you, fire at you, and flog you. Before proceeding, scavenge around until you have a healthy supply of grenades. When you're ready, creep towards the doors. If you’re quiet, you can run about halfway to the elevator before being detected. If you have full health you might just make it. If that isn’t working, then you’ll have to eliminate the threat as best as you can. Hang back as far as you can and snipe the Fighters standing on the left pillar. Then turn and snipe the ones on the pillar to the right of the doorway. If they aren’t visible, shoot the wall near them to get their attention. Hopefully you can take out the doorway guardians without alerting the rest of the crowd. When they are taken out, run through the doorway, making a beeline for the elevator. When you start taking fire, do a 180º and blast away with your shotgun while backpedaling to the elevator. Eventually, the cutscene will kick in. When all is said and done, passing this level requires not only a little knowledge, but also a lot of skills and some plain old dumb luck. Good luck.

Legendary Walkthrough
Wow, somebody really screwed up. The Flood has been released and now you're being ordered around by some AI to go kill a bunch of stuff for reasons you don't entirely understand. Sound familiar? Anyway, this level is full of Flood. Wave after endless wave of them. Soon you will know just how aptly they were named.

The Library
There are many reasons to dislike 343 Guilty Spark. The fact that he takes away your shotgun is one of my favorites. You should remember how to use the assault rifle on the Flood though. It's not that bad. And you do get a pistol, which you'll basically be keeping throughout the entire level.

Move forward past the two big vents in the wall and look back behind you to your left. Tucked away in the corner is the first you'll see of a new form of the Flood. This is the carrier form. Following in a great Bungie tradition, this enemy's only attack is to hobble towards you and explode. They release several infection Flood when they do this as well. So if you're anywhere nearby not only do you get your shields knocked out by the explosion, but you'll also immediately get reamed by the infection forms. Fortunately they're really slow. So not only can you get away from them pretty easily, but you can also lead their friends into the explosion when they do go off. Two rounds from the pistol will detonate them quite nicely. So whenever you see a whole mess of combat forms near a carrier, put a couple of bullets into him and BOOM! He takes out all his pals for you. If you want to save the ammo you can just run right past them as well. They flop over and start to blow as you get close, but by the time they actually explode you've run past them. Running up and jumping over them works well too. One thing that does not work well is blowing them up with a grenade. That tends to send them flying around the room like little bomblets. One will inevitably come down right next to you and explode.

Take out this first carrier however you want and let the little guys pop themselves on your shield. Melee as many as you can and run around to let your shield recharge as necessary.

There are two pairs of carrier Flood hiding around the corners ahead so be careful of running away from one and backing into another. Take these out however you want. Four carriers shouldn't be a problem if no one else is around.

Get your pistol ready and move ahead. There are two vents in the wall on the left past the previous carriers. When you walk near them, a squad of angry Flood will drop down. Inch forward until you see a signature on your motion tracker then back up and get ready for them. Target the carrier Flood and take them out as soon as they drop down. Hopefully you'll catch a few combat forms in the explosion. Empty the rest of the pistol clip as you're retreating and back up around a corner so the Flood have to come all the way around the corner to shoot at you. Get out your assault rifle and look for them approaching on your motion tracker. As soon as you see a body part, toss a grenade at the corner and start firing. Back up as they get closer and keep burning through rifle rounds. As you're backing up, swing around so that your back is towards the beginning of the level so you don't get stuck in a corner. Retreat all the way to the beginning if you have to. Once they stop coming move ahead and look for any carriers hobbling along. Here's a big hint for the rest of the level. Don't pop carrier Flood when they're standing in a pile of bodies. First of all, they'll scatter the weapons all over the place making it nearly impossible to find them when you need them. And secondly, they'll detonate any grenades nearby often catching you in a massive chain reaction. So if you see a carrier Flood coming towards you, look at the ground to be sure he has lots of space to explode before rupturing him.

So anyway, lure any leftover carriers into an open space and run by them or shoot them if you wish. Now that the area is secure, scavenge for a shotgun. Even if it only has a few rounds of ammo, it's better than your assault rifle. You may need to turn on your flashlight to scavenge well in here. Oh, and look for grenades and pistol ammo too of course.

Move along past the vents those last guys came out of and look ahead. Multiple waves of Flood are going to come out of the next set of vents. The first group is already there. Several combat forms are waiting to ambush you just on the other side of the sloping walls with the lights you have to walk between. Peek in between them and snipe anybody on the other side. Eventually you'll probably get the attention of the Flood hiding on the other side of the wall, so be careful. When they come, back up, wrap them around a corner, drop a grenade, and blast them with your shotgun. Now you can go back to the rest of the waves coming out of the vents.

Use the same strategy you did with the last group that dropped out of the vents. Target carriers near combat forms first and use the pistol until they start to get close. Then back up around a corner and wait for them. Drop a grenade and open up with the shotgun as they come around the corner after you. This simple strategy will get you through most of the encounters on this level. After each wave is destroyed, take a moment to scavenge and then walk up to the vents to set off the next wave. It is worth noting that the number of waves seems to vary somewhat. Sometimes they'll all come in just a couple of big groups. Other times they trickle out in several smaller waves.

Once you can safely walk around under the vents without triggering more Flood, the area is secure. Make one last sweep through the place looking for goodies then move ahead. You'll be going through a tunnel that leads to the atrium that houses the index. Use tunnels like this one as bottlenecks to concentrate the Flood in small spaces. They're much easier to deal with if they're only coming from one direction a few at a time. Move through the tunnel and get the attention of any combat forms ahead. Duck back into the tunnel and give them a face full of buckshot if they pursue you. Once they're gone, stay near the tunnel and snipe the carriers. Now you have a whole load of infection forms to deal with. You could just run around trying to melee them, recharging as necessary, but there's a quicker way. Pick up any old weapon lying around and use that on them. You'll want to conserve your pistol and shotgun ammo, but that doesn't mean you can't pick up a plasma pistol or assault rifle and use that to hose them down. Once they're mostly gone, toss whatever you used on them and pick back up your real weapon.

The way out of this chamber is another tunnel to the left. If you ever get lost or don't know which way to go, look for the Monitor flying around. He glows bright blue and will lead you in the right direction. Here's another tunnel for you. Move through it and a combat Flood will come leaping at you. Stop and put a shotgun shell into him as soon as he lands. Drop a grenade right on top of his corpse and back up. The grenade should take out any Flood that follow. On the other side of the tunnel straight ahead are more vents in the wall. This time several waves will be coming down. To activate a wave, you have to move forward to around the spot where you wasted that first Flood who jumped at you. So move ahead until you see Flood dropping down then retreat into the chamber with the index. Whip out your pistol, zoom in looking down the tunnel and snipe at any carrier Flood near other Flood. After a few shots, the rest of the wave will come running down the tunnel to get to you. Switch to your shotgun and let them have it. Drop grenades when necessary. After each wave, scavenge what you can, reload everything, and then do it again. After a whole lot of waves, they will stop coming. Move in and thoroughly scavenge the area. You should be doing pretty well by now on shotgun shells, pistol ammo, and grenades.

The hall ahead has another wave of Flood in store for you. Move along and you'll see an infected marine leaping towards you. Immediately start in on him with your pistol. From now on, I'm not going to always explicitly mention that you should target carrier Flood when they're near combat forms. This should just always be a priority for the rest of the game. Anyway, keep backing up and firing until they start to get close. Back up through the tunnel into the index chamber and wait for them. When they come into the tunnel after you, drop a grenade and start firing. After they've been reduced to snot, move ahead. There will be one last combat Flood up on the sloping wall thingy on the right. Snipe him down with your pistol then head over to the giant door on the left.

Wait around by the door for the Monitor to return. You can continue down the hall if you want, but the only thing you'll find is a hoard of infection forms and nothing useful. So unless you just really like to watch them pop, I wouldn't bother.

Move through the door as it opens and you'll come to another huge hall. Here you have a choice. The Monitor is going right and that's the way ahead. But there's a health pack to the left, though it's guarded by about a hundred infection Flood. If you're really low on health, you should probably get the health pack before moving on. It's tucked away in the back corner as far away as possible. You'll activate a whole slew of the little guys, so lead them back to where you were and then pop them however you want. Grab a spare weapon, melee them, whatever. If you're in the blue, don't bother.

Moving along you'll find some more Flood to kill. Move slowly ahead and keep an eye on the motion tracker. As soon as you register movement, retreat. Keep your pistol up and start shooting Flood as they land. Move around a corner and blast them as they come around for you. Give the carriers some space then kill them off too. Same tactics you've been using.

The next battle is a trap. Move ahead past the previous skirmish and stay frosty. As soon as you see blips on your tracker, turn around and run back towards the big door. Flood will be dropping down in front of and behind you. Blast through the ones in your way with your shotgun then turn around and use your old tactics on the others. Pistol, corner, shotgun. You know the routine. And as always, remember to scavenge thoroughly.

Ahead the path will take a turn to the left. Many waves of Flood will come dropping down from vents high up in the walls here, so be careful. As soon as you see them, run away. Don't engage them from around the closest corner. You'll kill them off more quickly, but stand a greater chance of getting overwhelmed. Get a bit of distance on them then get their attention with your pistol. Apply standard Flood-killing tactics retreating as necessary. Move back up to set off the next wave. Repeat until no more come down to play with you.

Now you can safely take that turn to the left. At the end of this hall is another turn to the left, but before you get there a small wave of Flood will come out. Nothing you can't handle. Just back up when you see them coming and gun them down with your pistol.

Move past the bodies and the path will take you down a long hall. You will get a checkpoint then the Monitor will fly away and head through a vent at the end of the hall. One big group of Flood is about to come out of that vent. Another group will come from around the corner ahead on the right. Back up as they drop down and toss a grenade into the middle of either group. Keep nailing them with the pistol and toss another grenade if necessary. Back up around the corner if any combat Flood get through and waste them with your shotgun. Mop up the carriers and infection Flood and scavenge.

Just around the corner ahead is a health pack. As you move forward though three combat Flood will come leaping at you. Put a shotgun round into each of them as you back up around the corner. Three or four more combat Flood will soon come around following the previous ones, so put them each down in turn.

Move ahead now and grab the health pack if you need it. Down the nearby ramp is an over shield. You might want to hold off on grabbing it. The next battle will hopefully be very easy. Move into the next section down the hall. Several pillars and structures, but no bad guys. The section ahead has a little hallway off to the left. It's full of Flood. Slowly work your way around until you can just barely see a bit of Flood down there without setting them off. Bounce a frag grenade or two right into the middle of them. After they've gone off, move into this section and you'll trigger some carrier Flood to drop in from on your right. Any survivors from the grenades will come out as well. Take them down with your pistol/shotgun combo as usual.

If you haven't grabbed the over shield already, do so now. Move ahead past the previous fight until you see Flood dropping down far ahead in front of you. They are the first of many, but ignore them for now. This is another trap. Several carriers will appear behind you, so turn around and be ready for them. Move back towards where the over shield was and take each carrier out from a safe distance. Get rid of any infection forms quickly. You can probably afford to spare a few rounds on them by now. Now turn your attention to those guys that dropped down ahead of you. If they followed you back here, take them out with the shotgun as soon as possible. Otherwise, snipe at them from a manageable distance. They will be followed by many more waves of Flood all dropping down from the same vents at the end of the hall. Slowly whittle them down using the same tactics you've grown accustomed too. You will burn through a lot of ammunition, but eventually they will stop coming. Wade through the pile of bodies and restock your supplies.

Move ahead to the end of the hall and peek in all the nooks and crannies. There is a small group of carrier Flood here and they can sneak up on you if you're not careful. Take them out however you want and dispose of the infection forms.

You have one last fight ahead before you're done with the first floor. And you get some help this time. Move along and a large group of Flood will come down the hall after you while a group of the Monitor's Sentinels move in from the side to help. Plant a few grenades right in the middle of the incoming Flood then duck back into the area the Sentinels came from for cover. Hopefully the Sentinels will take out the rest of the Flood for you. Once the battle stops, go see who won. If there are Flood left, they should be easy prey for you by now. Scavenge through the bodies thoroughly then move ahead onto the lift to the second floor.

Wait, It Gets Worse!
Step off the elevator and move ahead into the hall. Several carrier Flood will come out of the vent to your right, so watch for them. Retreat towards the elevator and pop a few caps in their ass. Mop up the infection forms. Now you're free to cruise down the hall. You'll pick up a new batch of Sentinels along the way.

At the end of the hall the path takes a turn to the left. You'll come across several carrier forms wandering around after the turn. Let the Sentinels take care of them while you take a look around. There are two health packs down a ramp in this first area. You can grab one now if you need it. Move ahead until the Monitor leaves and you get the message to hold your position. Immediately turn around and hurry back towards the area with the two health packs. This is another trap. If you move ahead now a whole ton of Flood will come out of the woodwork and put the smack down on you. Better to stay back while the Monitor does his work. Once he comes back and opens the big door, you can move ahead safely. The massive horde of Flood won't show up. Of course if you want to fight them, you can do so quite effectively using the same tactics you honed on the previous groups of Flood.

Either way eventually the Monitor will open the door ahead and you'll have another fight on your hands. The Sentinels will move through without you and might even start blasting at a group of distant Flood. You have two options now. You can run ahead and take a shortcut, or you can follow the intended path and face three more battles with the Flood. I'll cover both options starting with the shortcut.

If you want an easier time, run through the giant doorway past the Sentinels and right up to the edge overlooking the central chamber. Turn ninety degrees to your right and you will see a short, sloped wall. Run up and jump on top of it. It's high, but you can get up there. Hop down on the other side and continue along this little inner path around the central chamber. This same shortcut will work on the third floor when you have to get to the other side of the chamber up there. Keep on hopping until you can get back to the outer hall on your right. There's another huge door here, so walk up to it and the Monitor will pull his usual trick of making you wait for him to open it.

If you want to fight your way ahead, move up to help the Sentinels as quickly as possible. Notice the health pack and grenades just before the door on the way. Zoom in and snipe until they get close enough to start battling the Sentinels. It might be a little hard to aim accurately in all the confusion, but toss a grenade or two at the main group of Flood and empty a few pistol clips into the mob until they thin out or start coming for you. Then you can fall back and take them out with your shotgun as they get close. Hopefully most of the Sentinels survived.

Scavenge from the fallen Flood then move ahead and zoom in on the path ahead with your pistol. More Flood will come into view and start moving towards you. Shoot as quickly and accurately as you can. Definitely look for carriers to pop in the group. Once they get close they tend to bunch up and start firing at you and the Sentinels. Toss a grenade into the pack and keep firing. Once it goes off, run in and clean house with your shotgun. Scavenge and move ahead.

The next group includes one of the most despised enemies in the game. A Flood with a rocket launcher. These guys are deadly accurate and aren't afraid to take out all of their friends as long as they catch you in the explosion. Zoom in like you did before and take him out as soon as possible. Finish off the rest of the Flood like you did the previous ones. Keep on them with the pistol until they get close and bunch up. Grenade them then follow up with the shotgun. This time there may not be any Sentinels left to distract them, so be ready to take a lot of heat once the last of them goes down. Back up and keep doling out shotgun shells until they're all dead. Scavenge the area thoroughly and find that rocket launcher. Switch out your pistol for it. Rocket launchers on this level aren't really worth saving. Pick them up and use them on the first enemies you see then toss them and get your pistol back. You also don't want to run all the way back here to get your pistol. So keep switching out the two weapons, moving forward. If you get the rhythm right, you can move pretty quickly, constantly tossing one weapon in front of you while picking up another. Of course you have to stop when you need to turn, but you don't need to carry it far. Just past the next big door is fine. This trick is obviously very useful throughout the game, but it's especially useful for getting rocket launchers around on this level.

So now regardless of which route you took, you should be ready to move through the giant door once the Monitor opens it for you. Again, you will have a choice: right or left. This time right is the only way to go. There's nothing but infection forms to the left. Get that rocket launcher ready (if you have one). Run ahead and as you round the corner a whole bunch of combat forms will come running up a ramp in front of you. Send a rocket right into the middle of them and watch them fly. Use up the rest of the rockets on anything nearby then go back and get your pistol. If you don't have a rocket launcher, a well-placed grenade works just as well. Make sure the area up here has been thoroughly cleansed then grab the health pack on the backside of one of the nearby pillars. Next, head down the ramp to the tunnels below.

There are several carrier Flood down here, but you can take them out from a safe distance. Just be careful going around corners. As you approach the end of the tunnel, get your shotgun ready. As you move out into the open, a combat form will drop down right in front of you. Put a shell into him then switch to your pistol and retreat into the tunnel. Zoom in and take out anything that comes down after you. If a whole lot of Flood come down the tunnel at once, you may have to back up all the way around the corner and shotgun them as they come around. Move ahead up the ramp and look for more Flood. Retreat into the tunnel as necessary and eventually the area up here will be clear of Flood.

Move around the corner ahead to trigger the next wave of Flood. They will drop down from near the ceiling. Back up to where the ramp meets the floor you're on and wait for them to come around the corner. Apply shotgun shells and grenades as necessary. Once you've dispatched each wave, move up to trigger the next. Use the same tactics for each and if things get too hot, feel free to move back into the tunnel. It's much safer in there. Scavenge through the bodies once they stop coming.

Move ahead, but be careful. The path will take a turn to the right after you pass the vents the last guys came out of. At the end of this next hall lurks another Flood with a rocket launcher. There are also many carrier forms nearby, so zoom in with your pistol and carefully peek around enough to pop a few carriers. Keep moving around sniping anything you can. If they come after you, use your motion tracker and run them into either a grenade or your shotgun. If you can take them all out from a distance, that's even better. If you see a rocket coming down the hall, run away! Once these guys are toast, move ahead and collect the goodies. There's a health pack at the end of the hall on the left. There should also be two rocket launchers lying around. Don't pick up either yet. Move around the corner ahead and a small group of Flood will come after you. These guys aren't worth wasting a rocket on. Just back up around a corner and shotgun them. One infected marine will stay on the little wall around the corner instead of pursuing you, so peek around and snipe him down. Now you can switch out your pistol for a rocket launcher. Be careful not to run over one of the launchers while you're carrying the other. You'll pick up the extra ammo, but waste any rockets that are already chambered. It's not a big deal, but, hey, one rocket can be a big help. So put your pistol and one rocket launcher in a safe place then move ahead.

Move through the section with the ramp to the section with the pillars and things. As you approach, a few carriers will appear to the left and a few combat forms will drop down from the vent on the right. Send a rocket towards the middle of the combat Flood then retreat. Get a bit of distance then finish off anybody who comes after you with your shotgun. Reload everything then do it again. Once you run out of ammo in one rocket launcher switch it out for some random weapon lying around then switch that out for the other rocket launcher. Now you'll have more rockets and can continue blowing things up. Grab your old pistol once you've expended both rocket launchers. By the time you get your pistol back, there shouldn't be any more Flood coming out of those vents.

Move to the end of the hall and a whole ton of carriers will appear out of nowhere. Turn back the way you came and retreat, carefully blasting through a couple of them on the way. Once you're quite certain all of the carriers are behind you, turn around and pick them off from a distance. As long as you aren't surrounded, these guys should be pretty easy.

Now you're clear to move onto the elevator and head to the next floor. You'll encounter some minor resistance if you wait around near the elevator, but nothing really nasty. Just run straight ahead and you'll breeze past these losers.

But I Don't Want to Ride the Elevator!
Step off the elevator and head into the hall. Moving along, you'll pick up a shiny new batch of Sentinels. Lead them ahead around the corner and you'll encounter a small group of Flood. The Sentinels can sometimes win this battle by themselves, but you'd better give them some help. Just run up and off a couple of Flood nearby then let them finish off the rest. After they've stopped firing, pick off any Flood that may be out of their sight. There's a health pack up on the little sloped wall on the right past the ramp. And there's a rocket launcher tucked away at the end of the hall on the left. Look for it next to a Flood corpse. Rocket launchers are always handy, so you might want to bring this along. Try the trick of continually dropping weapons in front of you as you move to get the launcher, pistol, and shotgun all down the ramp and into the tunnel with you. Be sure to scavenge here as well, since you can get shotgun shells and pistol ammo.

Down the tunnel and around the corner is a long corridor with several combat forms at the end. Zoom in with your pistol and take them all out from a distance. Move forward a bit and a horde of infection forms will appear. Shoot a few bullets into the mass and let the rest pop themselves on your shield. There are a few carriers around the corner, so peek around and take them out too.

As you move ahead you'll see a ramp leading up out of the tunnel. There's a battle starting at the top that you may not want to get caught in. Peek out and try to gun down a few Flood, but retreat into the tunnel whenever things get even slightly nasty. Now would be a good time to use those rockets if you lugged them up here. Shoot them all off, then run back and pick your other weapon up again. Take advantage of the Sentinels as long as you can, but once they've been destroyed, get back in the tunnel. You can take out the rest of the Flood from here. Snipe with the pistol then back up around the corner and shotgun the rest. Scavenge. You know the drill.

Head away from your last battle and down the long hall. Keep going until you get the message to hold your position until the Monitor returns. Yeah, right. Don't hold your position. Run like hell back to the long hall you just came from. A big pile of Flood will come after you so toss grenades, aim for carriers, shotgun everybody, and keep retreating as long as necessary. After you finish off this initial wave, wait around in the hallway. Don't go back to area where you triggered the last group unless you're looking for another big fight. It may take a couple of minutes, but eventually the Monitor will come back and open the door ahead. Once he does so, you can move ahead without triggering any enemies. Snag the health pack if you need it.

Once again you have a choice of paths. You can run up to the edge of the chamber turn left and jump over the little wall. This maneuver was a good shortcut on the previous floor, but this time it will put you in a bad position, so I'm going to suggest you proceed the normal way.

Around the corner ahead to the left is yet another group of Flood. One of these guys has a rocket launcher, so gun them down fast. You might not want to use a grenade since that will blast the rocket launcher far away, and you're going to want it soon. So put these guys down quickly with your shotgun then toss your pistol and pick up the rocket launcher.

Ahead another small group of Flood will come running towards you. Use those rockets. Just blow these guys away. Go back and grab your pistol when you run out of rockets.

Move ahead. A few Flood will jump up onto some blocks in the area ahead. Send your last rockets at them if you have any left, then switch to your pistol. Take the rest of these guys out like normal. Pistol at long range then wrap them around a corner and hit 'em with the shottie.

Head through the big door and grab the health pack and grenades if you need them. Ahead a few Flood will jump out of one of the little trenches at you. Put each one down as they land then back up around a corner. More Flood will come around after you, but a few shotgun shells and possibly a grenade should finish them off easily enough. Peek out and snipe down the one Flood on the right wall that didn't hop down with his pals.

Ahead the path will turn left and multiple waves of bad guys will fall down from vents near the ceiling. You've been in situations like this before. Retreat so you only face one wave at a time then deal with them as usual.

After you've cleared these guys out, you have a bit of a walk. Keep moving along and you'll come upon some Flood bodies. Scavenge around a bit. There should be some ammo for what you're carrying around here.

After that, you'll come to a big door that's open just enough for you to get through into the next room. As you walk through the door, look to your right. There's a little alcove there that you will be retreating back to very shortly. In this room there are three health packs. Two are behind the columns to the left. Grab one now if you want. Once you're set, walk under the Monitor. He's waiting by the other big door. As soon as he moves away and you get the message to wait, run like hell back to that little alcove. You'll see the door you came through closing. Tons of Flood are about to fill this room. And if you kill them, more and more waves will come. This battle can be one of the toughest in the game. Or it can ridiculously easy. If you stay in that alcove and keep your mouth shut, they won't ever know you're there.

Wait around for a couple of minutes and eventually the Monitor will come back and open the door ahead. The Flood will all follow him through the door and begin battling a contingent of Sentinels. While they're running away, you can move in behind them and nail them once they bunch up under the Sentinels. Toss a grenade into the middle of them and start blasting with the shotgun. If you keep getting your butt kicked here, just wait a little longer before coming out of your hiding place and the Sentinels will do more of the work for you.

After everybody's dead, scavenge and look for a rocket launcher. There should be one among the bodies. Snag it and drop your pistol, but of course remember where since you'll be grabbing it again in a second. And don't forget about those health packs back in the room of death. Go grab one if you need it.

Rounding the corner the Sentinels will begin firing upon yet another group of Flood. Wait around for a second and the Flood will tend to bunch up on the ground. Send a rocket right into the middle of them. Wait around a few more seconds and the Flood will just keep coming. Once they've bunched up a second time send 'em another rocket. Fire off any extra rockets then run in and take out any survivors with your shotgun up close. Go back and grab your pistol again.

Keep moving and you can run right onto the elevator to finish out this floor. A few pathetic carriers might drop down nearby, but I think you can handle them.

Fourth Floor: Tools, Guns, Keys to Super Weapons
OK, last floor. Move ahead into the hall. There are several carriers hiding around the corners here, so be cautious. A Sentinel here will provide a bit of help, but you'll have to pop most of these guys. There will also be a health pack right in front of you as you step into the hall. There will probably be a carrier left at the end of the hall as well, so check those nooks and crannies before moving on.

This next battle is a tough one, but use the same old tactics and you'll come out on top. Run around the corner and a big wave of Flood will drop down from vents near the ceiling. Sound familiar? Just fall back like normal and take them out as they come around the corner after you. These waves are pretty big and there are a lot of them, so be generous with the firepower. Retreat all the way back to the elevator if you have to. After a great many waves, they'll stop coming and the way will be clear. Scavenge around thoroughly then move ahead.

Head down the tunnel and take out any carriers lurking down here. This next battle can be very annoying because it's a trap. As you exit the tunnel, several carriers will spawn behind you. So when you try to retreat, BOOM, you get blown to bits. You can handle the situation one of two ways. You can just not retreat into the tunnel. Run up and dive into the melee, blasting a few guys, then running around a corner up there for safety. It's actually not as difficult as it sounds. This is the easier route in my opinion. Many, many Flood will come after you, but you won't face more then a few at a time and as long as you stay around a corner, you'll be fine. If you're more methodical and need the shelter of the tunnel, you'll have to run up and peek out then run back and blast the carriers waiting in the tunnel. Once they've detonated, run through the mess and get you pistol ready for any pursuers. A few Flood will probably come down with you and you can take them out. Then you'll have to repeat the process again, and again. There are many waves of carriers set to spawn behind you, but eventually you can kill them all and clear the path behind you. Each time you run back through them a few Flood will follow. So you should be able to take out the rest of the guys up top with little trouble. Once you're ready to leave the tunnel for good, there's a health pack lying around for you. And there's another one in the ditch ahead if you've already used that one up.

Move along around another corner or two and eventually a slew of carriers will drop down all around you. Turn around and blast your way through a couple to clear a path then take the rest out long range once they're all safely on one side of you. Past the carriers you'll run into another small group of Flood as you round a corner. Take these guys out as usual. Snipe a bit if you can then hit them as they come around the corner after you. There are several carriers amongst the group to work with as well.

Look behind the pillars ahead and you'll find a rocket launcher and a health pack. Swap out your pistol for the rocket launcher and toss them around until your pistol is in a more open area closer to the big door ahead. You're going to want it back after you fire off those rockets.

Alright. This is it. The last battle of the level. Move towards the big door to begin. The door will only open part way before Flood start jumping through to get to you. Put a shotgun shell into each of these guys as soon as they land. Once the door fully opens, a deluge of Flood will come after you. Toss a couple of grenades and shoot two rockets into the approaching mass. Retreat and reload. Don't get backed up into a corner. As long as you stay on the path you used to get here, you'll be ok. Just keep backing up and going through rockets. Once you're out of rockets, run back and grab your pistol. Keep retreating and reload after each couple of shotgun shells so there isn't too long a pause in the damage you're dishing out. Use up all the grenades you have if you need to. Toss them at any groups. Eventually, you'll be left with a long string of Flood corpses and little ammo. Scavenge through the bodies moving back up to the last big door. Just after the door there are a couple of Flood perched up on ledges on either side of the door. Toss a grenade at them or gun them down with your pistol. Be careful not to move into the next room or you'll risk triggering the next wave.

Now once again you have two choices. An easy route and a route that allows you the satisfaction of killing everything. I'll go over the easy route first.

If you want to just run for it, head out the door and take a left. That's right. Not towards the index. Just run as fast as you can into the chamber on the left. Once you're in there, head towards the edge overlooking the central area with the index. Once you're on the edge, turn ninety degrees to your right and you will see a little sloped wall. Run up and jump on top of it. It's high, but you can get up there. Fall down on the other side and make a beak for the index. You should get there fairly easily.

If you want to be more thorough, you can deal with the rest of these Flood in the traditional way. Move into the chamber and more waves of Flood will come from the area near the index. Fortunately none of these are as nasty as that initial wave. Just keep cool and go through the ammo. Scavenge whenever there is a brief lull. There are many, many waves of enemies, but none of them is really that difficult. Just stick to your old tactics of retreating and wrapping them around corners and you'll do fine. Eventually you will have killed every Flood in the area. Once you've accomplished that, the index is yours for the taking. Saunter on up and snatch it.

Congratulations. Now that you're a both a seasoned Flood-killer and Covie-killer, the rest of the game should be a breeze, right?

Eggs
on the first elevator you ride get it just high enough to where you can walk under it, once under it will start to go back up, jump into the blue light that represents a grav lift, you will fall to your death but at the bottom you will see a spinning 343 Guilty Spark who will even talk.

through out the level there are spawn points for flood that you can re activate after going through them the first time

On all the lifts, in the center there is a four leaf clover.