Upon completing it on the Normal, Heroic, or Legendary difficulties, the player will earn the Last Stand achievement and 40 Gamerscore. Earning over 50,000 points in the campaign meta-game on this level will give the player the Vanguard achievement and 10 Gamerscore. It is the longest level in Halo 3. This level is significant as it is the Covenant's last stand. After the Covenant have been defeated, there is only one last threat the UNSC and Sangheili have to deal with: the Flood.
On the Ark, the Master Chief must stop the Prophet of Truth from firing the rings. Before reaching Truth, the UNSC and Sangheili forces must deactivate three towers powering the defensive barrier protecting the Prophet's citadel. They deactivate two towers, but the initial assault on the third tower fails, resulting in Sergeant Johnson being taken prisoner. The Master Chief joins forces with the Arbiter and the other Sangheili and they launch a joint assault on the third tower. The Chief completes Johnson's task and deactivates the final tower, lowering the barrier. Before the Shadow of Intent can begin its assault, however, the Flood-infested High Charity emerges from slipspace and crashes into the Ark, damaging the Shadow of Intent in the process. The UNSC and Sangheili forces make one final ground assault on the citadel, facing off against a massive vehicular Covenant force, including two Scarabs at once.
After defeating the Covenant forces outside, the Master Chief and the Arbiter enter the citadel, only to discover that Truth is moments away from using Sergeant Johnson to activate the Halo Array. In a desperate effort to stop Truth, Miranda Keyes crash lands her Pelican into the citadel's control room and attempts to rescue Johnson. However, she is killed by Truth who then forces Johnson to activate the Ark. United by the common purpose of stopping the rings, the Gravemind offers an alliance with the Chief and the Arbiter. With the Flood's help, the Chief and the Arbiter defeat Truth's remaining followers and shut down the Halos. The Arbiter then personally executes Truth, ending the Human-Covenant war at last. Moments later, however, the Gravemind and the Flood turn against them. Johnson escapes in Keyes' Pelican while the Chief and the Arbiter fight their way back outside. Upon escaping, they finally discover Cortana's solution to the Flood: a newly-constructed Halo ring built to replace the destroyed Installation 04. When fired, the Halo will cleanse the Flood infestation upon the Ark while leaving the rest of the galaxy unharmed. The Chief realizes that in order to fire it, he must rescue Cortana from High Charity as she still possesses the Activation Index from the first Halo ring.
Three teams. Three towers.
Five Pelicans fly in. They are followed by two Sangheili Phantoms. Behind them is the Sangheili CAS-class assault carrier Shadow of Intent. The view changes to a large energy barrier surrounded by Covenant forces
A patrolling Unggoy spots the dropships as they approach the mainland. It jumps and cowers.
Gunfire hits one of the trailing Pelican's engines, causing it to collide into Hocus' Pelican, tossing its Warthog out onto the ground. The second Pelican swerves out of control and drops its Warthog as well.
The Pelican drops out of sight followed by the sound of a crash and a muffled explosion.
Chief grabs a Spartan Laser as his Pelican makes a rough landing.
The Master Chief and the ODSTs storm the beach, eliminate the enemy infantry - including a Jiralhanae War Chieftain and destroy the Anti-Air Wraith.
The Shadow of Intent starts firing plasma torpedoes at the barrier.
A Pelican drops off a Mongoose and Warthog for the Chief and his Squad. If the existing squad have all died, replacements will also be dropped off.
They mount up and head off for the First Tower.
As the Chief drives up the hill towards the 1st generator, he sees the Sangheili Phantoms battling with the other Covenant loyalist Phantoms near the second tower.
(Co-op Change) Commander Keyes (COM): "Good. The Elites have touched down at number 2."
The strike team reaches the First Tower.
Keyes' Pelican drops off weapons.
The Chief eliminates the Covenant troops guarding the door.
Master Chief gets inside and secures the bottom floor.
The ODST and/or Marines hold the bottom floor while the Chief takes the elevator to the top floor.
The Master Chief deactivates Tower 1.
Tower 1 shuts down.
(Co-op change) Commander Keyes (COM): "Good work, Chief! That's one. The Elites should be just about to..."
Tower 2 shuts down.
The Chief and Commander Keyes watch Tower 3 for a moment. It remains active.
(Co-op change) Commander Keyes (COM): "Chief, you need to link up with the Elites and proceed directly to the Third Tower. Make your way back to the beach."
The Chief hurries back to the elevator and heads back down. After clearing another group of Kig-Yar and Unggoy attacking the Marines holding the lower floor, the Chief and his squad get back outside to their vehicles, or meet up with transport if they have no vehicles left.
The Chief and the Marines head back to the beach. Once there, the Chief and his accompanying soldiers meet up with the Hornets and other Marines who held the beach.
If You Want It Done Right...
Close air support.
The Chief gets in a Hornet. He assists the other Hornets in clearing the airspace of Tower 2, which is heavily saturated with Banshees and a single Phantom.
If the Chief tries to land at the Second Tower:
They proceed to Tower 3, where they meet heavy resistance both in the air and on the ground.
A pair of Anti-Air Wraiths, a standard Wraith, Shade turrets and a large Jiralhanae pack lead by a War Chieftain guard the Third Tower. After the UNSC airborne forces take out the Anti-Air Wraiths, the Sangheili Phantoms arrive and drop off Thel 'Vadam and a group of Sangheili. The Chief uses his Hornet to eliminate any remaining enemy armor and infantry. He then lands the Hornet and joins the Sangheili on the ground. The bodies of Johnson's team litter the tower's entrance, but Johnson himself is nowhere to be found.
Marines from the Pelicans and Hornets follow up, and secure the perimeter. The Chief, 'Vadam, and the Sangheili push on inside the tower, encountering a small pack of Jiralhanae at the doorway. Inside, they battle a swarm of Yanme'e and a Mgalekgolo pair. Eventually clearing out the opposition, the team move deeper inside and encounter a larger pack of Jiralhanae, followed by another swarm of Yanme'e. The Chief, 'Vadam and their allies overcome the defenders and secure the bottom floor and the elevator.
'Vadam and his Sangheili hold the lower level while the Master Chief heads up. The Chief secures the top floor, after defeating a Jiralhanae War Chieftain wielding a plasma turret and a squad of Jiralhanae Stalkers.
The Chief deactivates the Third Tower.
The barrier falls. The Shadow of Intent advances on the Citadel.
Debris from High Charity strikes right through the Shadow of Intent's hull. A Flood dispersal pod then breaks apart in midair. Part of the pod crashes through the window right above the Chief. It stops as it hits the elevator window, glowing eerily. The Chief raises his rifle and prepares to engage the enemy he knows too well.
Flood forms swarm towards the lone Spartan, infecting the corpses of the Jiralhanae in the room. Soon eliminating the hostiles in the area, the Chief then takes the elevator back down.
The Chief links up with the Sangheili and the Arbiter, who are trying to hold back encroaching Flood forms. After clearing the room, they head back outside, eliminating more Flood forces (including several carrier forms). Arriving outside, they assist Marines engaged in combat with the Flood. A Sangheili Phantom arrives to pick up Thel 'Vadam. The Phantom's side gunner helps clear out any remaining Flood.
'Vadam takes 343 Guilty Spark with him. Meanwhile, Pelicans drop an Gauss Warthog, a Mongoose and a Scorpion tank for the assault on the Citadel. The Chief, the Marines\ and the remaining Sangheili mount up.
Storm the Citadel.
The assault team advances across the cliff, facing infantry, Ghosts, Shade turrets, deployable lookout towers, Prowlers, and a Wraith. Once the team breaks through the Covenant defenses, they meet up with two Hornet gunships near the route down into the clearing.
The Chief engages the Scarabs. The Assault Team backs him up: The Scorpion tank fires from a far range, while the Warthog and the Mongoose move about under the Scarabs to assist Chief in taking their legs down. They are soon joined by a second Warthog. The Pelican and the other Hornets engage the Scarabs from the air. Several enemy Ghosts, Banshees and another Prowler defend the Scarabs.
The Chief takes out the first Scarab.
The Chief takes out the second Scarab.
If any minor Covenant resistance on the ground is left:
A Sangheili Phantom decloaks and arrives at the platform leading to the entrance of the Citadel, dropping off Thel 'Vadam and 343 Guilty Spark. Any surviving enemy Banshees will flee at this point.
If the Chief isn't there when 'Vadam lands:
If the Chief stalls:
The Chief lands and meets 'Vadam and 343 Guilty Spark at the top of the platform.
Spark activates a light bridge. The Chief and 'Vadam cross it and enter the Citadel alone. The door they entered through closes and bolts up. The entrance is a large hallway with viewscreens mounted along the walls.
Viewscreens around the Chief light up. The Prophet of Truth is seen making another speech. The Chief and 'Vadam hurry to find a way up.
Master Chief and 'Vadam discover an elevator with a screen in front of it showing Sergeant Johnson held aloft by a Jiralhanae. Johnson punches the Jiralhanae in the face, to no effect.
They look up. The height is phenomenal.
The view changes to the Control Center. Johnson is thrown to the floor.
A Jiralhanae Chieftain gives him an amused huff, then picks him up around the neck and begins to strangle him.
Truth turns around and sees what is happening.
He turns back to the Ark's activation console and speaks quietly.
The Chieftain slams Johnson's head into the solid holographic console.
Truth leans forward so only Johnson can hear him.
A Pelican appears behind them unnoticed and rapidly approaches the main window.
The Pelican smashes through the window and crashes onto the ledge next to them, slamming into a Jiralhanae and sending it flying. Scene fades to black briefly.
Johnson climbs up from behind the control terminal, clutching his side.
More Jiralhanae surround Miranda and Johnson. Miranda fires at the closest Jiralhanae with her shotgun. Its armor is damaged, but it remains standing.
Keyes draws a pistol and aims her weapons both ways.
Keyes pauses and lowers her weapons. She looks at her pistol.
She reluctantly aims the pistol at Johnson. He staggers towards her.
Keyes hesitates, lowering her pistol slightly with sadness on her face.
Keyes straightens up and aims. Several Spiker shots are heard. Keyes gasps in pain and drops her weapons. Johnson starts to run to her aid.
A Jiralhanae Captain restrains Johnson, who struggles, horrified. Keyes falls to her knees, collapses and dies with five glowing spikes in her back. Truth walks on screen gingerly holding a Spiker in one hand. He looks down at Keyes.
He drops the Spiker, and shakes a fist to emphasize his speech.
Truth walks up to Johnson, who is still being restrained by the Jiralhanae.
Sergeant Johnson is brought up to the control panel.
He forces Johnson's hand down on the panel with a smug look. Johnson, still overcome with grief and shock, doesn't resist. Instantly, the Control Terminal begins to change and heighten. Truth raises his arms in triumph. The scene moves down the corridor, as six out of the seven holographic Halo rings light up one by one (Installation 04 has not yet been replaced, so its ring does not light up). At the end of the corridor, the Master Chief and Thel 'Vadam emerge from the lift. Two Flood tank forms drop from above. The Master Chief draws his assault rifle and aims, and 'Vadam activates his energy sword.
Note: In the subtitles, the Gravemind says "stop" instead of "halt."
The pair lower their weapons cautiously. Pod infectors scurry between their feet toward their common enemy. The Master Chief and 'Vadam look at each other, obviously not trusting the Flood, but knowing they have no other choice.
The Master Chief, the Arbiter, and the Flood begin their final assault on Truth. Three bridges stand between them and the Control Center. Resistance on the first bridge consists of Unggoy and Kig-Yar infantry led by a single Jiralhanae Captain, backed up by Unggoy Heavies. The Chief and his allies quickly defeat these enemies and cross the first bridge.
The Chief enters a room with holograms of Truth in the Forerunner systems.
At the second bridge, the Chief and 'Vadam encounter the final Covenant defenders - including a Jiralhanae Chieftain wielding a gravity hammer and his Bodyguards, with Jump Pack Brutes as the main counter-attack force (on higher difficulties, the Jiralhanae are supported by a pair of Unggoy Heavies armed with fuel rod guns). With the help of the Flood, the Master Chief and the Arbiter defeat the last of Truth's followers. They cross the second bridge.
In the second room, Truth's holograms broadcast a final message.
Resistance on the third bridge has already been crushed by the Flood. The Chief and the Arbiter step over the bodies of fallen Jiralhanae, Unggoy, and combat forms and finally reach the Control Center. A large gap is now all that stands between them and Truth. The Chief activates a light bridge, allowing them to cross.
The Master Chief and Thel 'Vadam cross the light bridge. They pass by an inert Flood corpse, and come across a distraught Sergeant Johnson who is resting Miranda Keyes' lifeless body on his lap by her head next to the Pelican. The pair stop and stare into Keyes' empty eyes, until Johnson closes them gently.
The Chief continues to stare at Miranda, shoulders slumped, obviously disheartened, while 'Vadam approaches the crawling form of Truth, his energy sword turned off but at the ready.
The Arbiter grabs Truth by the throat and points his currently deactivated sword in the Prophet's face.
Flood biomass suddenly erupts from Truth's head. Spores spew from his mouth. The Prophet is infected.
At this moment, 'Vadam draws his energy sword back and activates it, ready to kill his former leader. The Master Chief points his assault rifle at Truth in case he is completely taken over by the Flood.
Truth regains control of his body.
Tentacles begin to sprout on Truth as the Flood infection progresses.
The Chief approaches the Ark's control panel, ready to deactivate it.
The Chief deactivates the Ark. The holographic Halo rings dim. The Flood body begins to stir.
'Vadam releases Truth briefly, then viciously grabs his neck from behind. Truth's crown falls off as he pitifully gasps for air, trying to grab 'Vadam's hand.
'Vadam stabs his sword through Truth's back. It goes clean through him; the two points of the energy sword pierce through his chest as he writhes and screams in pain. Flood spores shoot out of his mouth and the infection lets out a pitiful squeal as both it and its host die. The last of the Hierarchs is dead.
The Arbiter pulls his sword out and lets Truth's corpse fall to the floor. He lets out a roar of triumph and deactivates his sword. He then turns to the Chief. The Chief gives the Sangheili a nod, acknowledging him for ending the life of the Prophet who declared war on humanity; they then turn to see Johnson carrying Keyes' body into the Pelican. There is a moment of silence as they realize their victory has not been without loss, but the Human-Covenant War is finally over.
Suddenly, the ground begins to tremble, and massive tentacles rise up all around them. Chief wields his assault rifle and 'Vadam reactivates his sword. They both stare up at the tentacles which are now reaching high above them. The Gravemind laughs maniacally.
Johnson leaps into the Pelican's cockpit and starts to take off, heading for the hole in the window that Keyes made earlier. The Chief climbs onto the control panel of the Ark and jumps up, grabbing onto the departing Pelican's landing gear. 'Vadam deactivates his sword and grabs the Chief's hand. Just before the Pelican can get out, the tentacles knock both of them off. The Pelican spirals out of control and falls out of sight. 'Vadam and the Chief land in a heap on the Citadel's floor. The Gravemind's tentacles swerve around them and multiple Flood forms can be heard approaching.
The Chief and 'Vadam get back up. 'Vadam reactivates his sword, and the Chief takes aim with his assault rifle. They come back to back.
For a moment, the tentacles appear poised to strike. Then - as if sensing a threat (possibly the Sentinels) - the Gravemind suddenly retreats, leaving its minions behind to deal with the pair. Two combat forms jump up from behind the Control Panel.
The Chief and 'Vadam kill the two combat forms and cross back over the light bridge. Both heroes fight their way through hordes of Flood, which have betrayed them now that the Halo rings have been deactivated. Fortunately, Sentinels have arrived and are fighting the Flood.
The Chief reenters the room where Truth's first message was broadcasted.
Master Chief and Thel 'Vadam make it back to elevator. The lift is not working, so they jump down a shaft at the back of the room.
The Chief lands at the bottom of the shaft, landing in a room not unlike the entrances to the three shield towers. He looks beside him as the Arbiter comes down, and then stands up. A flickering, spooky image of Cortana appears in the hallway, running. She starts to turn the corner and disappears, after a split second. The Chief casually walks around the corner as though amused by Cortana's antics, but 'Vadam is confused.
With 'Vadam trailing far behind, the Chief looks around the corner. He sees a control panel. Cortana appears a second time, again for only a second, walking loftily (and spookily) towards it. She stops at the panel and disappears. The Master Chief goes to the panel and activates it.
A view screen slides open, the Chief and 'Vadam step out onto a balcony to watch as a massive structure rises up out of thick fog. It's a Halo ring, incomplete, rising from inside the Ark's Foundry. Cortana's plan is becoming clear.
'Vadam turns and looks at the Chief.
Spark hovers up from behind and comes up to the Chief.
He flies enthusiastically around the Chief and 'Vadam and then flies off towards his new Halo now talking to himself.
The Arbiter turns to the Chief.
They both turn to look at the crashed High Charity in the distance, realizing that Cortana still has the Activation Index required to activate the new Halo ring.
Fade to black.