From Halopedia, the Halo wiki
Two Betrayals is the eighth campaign level in Halo: Combat Evolved. This is the last level in which Jackals are fought. It is also the first level where Sentinels are hostile enemies instead of your allies.
The Master Chief, after teleporting back to the Control Room, proceeds to activate Installation 04. However, Cortana, who after spending twelve hours in the control room has discovered Halo's true purpose, stops him just in time. After stealing the Activation Index, she tells the Chief that Halo will wipe out all life in the galaxy, and turns the Chief against the Monitor who confirms Cortana's claims, confused that the Master Chief didn't already know this. Spark sends Sentinels to take the Spartan's head, and the AI inside his helmet, but they are quickly destroyed.
Cortana decides that they must destroy Halo to keep it from being fired and decides that the best course of action is to detonate the UNSC Pillar of Autumn's fusion engines which will destabilize the ring and cut through a number of primary systems. To buy them some time in case the Monitor finds another way to activate Halo, Cortana orders the Master Chief to disable the three phase pulse generators in the area to force the Monitor to make repairs before Halo can be fired. The Master Chief is forced to fight through a combination of Covenant, Flood and Sentinel forces and use Banshees to reach each generator which Cortana uses an EMP to disable. Cortana is able to use the Covenant battlenet to locate the Pillar of Autumn's crash site, but requires Captain Jacob Keyes or his command codes to activate the ship's self-destruct. After disabling the third pulse generator, Cortana is able to locate Keyes, who is still alive, onboard the Covenant CCS-class battlecruiser Truth and Reconciliation. At Cortana's suggestion, the Master Chief allows the AI to draw power from his suit to use Halo's teleportation grid to teleport them to the battlecruiser rather than calling for a ride which will take more time that they don't have.
Long shot of the Control Room. Master Chief and 343 Guilty Spark teleport in, obviously in the middle of a conversation, explaining something about the Flood.
Master Chief pauses as though sensing something is not quite right.
Master Chief and 343 Guilty Spark move up to the main control panel.
Master Chief takes the Index, and puts it into a slot on the console. Lights and holograms appear, but then fade.
Cortana suddenly appears over the console.
There is a flash of light, and 343 Guilty Spark is thrown back, and down to the ground.
The Activation Index hologram appears in Cortana's hand.
Cortana's avatar absorbs the Index.
The Chief brings both hands up in the middle of them as if to stop a fight, then turns back to face Cortana.
Cortana points at Spark. Master Chief hesitates, and then turns to 343 Guilty Spark.
Four Aggressor Sentinels float up behind 343 Guilty Spark, their beams aimed menacingly on the Chief.
Master Chief looks around at the Sentinels, and backs towards the panel. He takes Cortana's data crystal chip out of the console, and inserts it into his head.
343 Guilty Spark teleports away. The Chief readies his weapon.
The Sentinels open fire at the Chief, but are soon eliminated.
The Gun Pointed at the Head of the Universe
The Chief proceeds through the corridors, eliminating several Covenant patrols as well as the Sentinels that they are in combat with. Soon the Master Chief exits the structure into the snowy night sky.
The Spartan heads down the pyramid structure, eliminating more Covenant patrols.
The Chief flies to a platform protruding from the cliff, clears a lance of Covenant guarding it, and enters the room containing the Phase Pulse Generator.
The Chief steps into the generator. The ground shakes rapidly as a small explosion drains the Chief's energy shields.
More Sentinels emerge. The Chief takes them out, then exits the room and returns to the canyon.
Breaking Stuff to Look Tough
The Chief reaches the bridge in the middle of the canyon, meeting more Covenant troops.
After fighting through Covenant troops, the Chief sees a few Flood combat forms attacking more Covenant patrols. The Spartan fights his way across several bridges that he previously traversed on his way to the Control Room. Various Covenant soldiers including a Sangheili Zealot attempt to repulse overwhelming numbers of Flood. The Chief kills them all and eventually makes his way to the bottom of the canyon.
A large Covenant force defends the area, including a Wraith tank, several Shades and numerous infantry. The Chief manages to kill them all and leaves the area. Proceeding past the area where a Warthog lies overturned, the Spartan continues to the next area where he fights through another large contingent of Covenant forces, including another Wraith and two Mgalekgolo. Eventually the Chief is able to defeat all hostiles present, allowing him to commandeer a Banshee. The Chief uses the fighter to wipe out several Unggoy operated Shade turrets as well as several fuel rod gun wielders and their Sangheili Zealot commander.
If the player continues on to toward the third canyon, before disabling the second pulse generator:
The Chief enters the second generator room. An intense fight between Flood combat forms and Sentinels rages around the generator. After clearing the room, the Chief steps into the generator and disables the generator. Flood combat forms jumps out from holes in the wall while some enter the room through the door, including several wielding heavy weapons.
After clearing the room, the Chief returns outside.
The Tunnels Below
The Chief draws closer to the tunnel that leads to the third canyon.
A large number of Covenant troops are embroiled in a struggle with yet more Flood forms in the tunnel. Eventually killing all combatants as well as several more rocket launcher wielding combat forms further down the passage, the Chief finds another closed door. The door malfunctions, however, forcing the Chief to leave whatever vehicle he was using. Fighting his way through more Flood forms, the Chief eventually manages to leave the tunnel and exits into the third canyon.
The Chief witnesses a group of Covenant led by two Sangheili Zealots making a stand on a hill against hugely overwhelming numbers of Flood. Eliminating the survivors, the Chief exits into another valley where yet another battle is taking place. A nearby cave opening hosts a large supply of abandoned UNSC weapons and ammunition, allowing the Spartan the opportunity to resupply. Eventually the Chief enters a final valley where a group of Flood throw themselves at a mass of Covenant defenses, including two Wraith tanks, several Shade turrets and a large number of assorted infantry being commanded by a Sangheili Zealot. Later in the battle, a squad of Stealth Sangheili as well as another Zealot, a Mgalekgolo pair and more infantry emerge. After a protracted battle, the Chief is able to kill all foes in the area and enter a Banshee fighter. He flies to the platform that leads to the third generator. Sentinel Aggressors appear and fire at him. As he arrives at the room containing the third generator, Aggressors with energy shielding appear. He eliminates the Aggressors and disables the final generator.
The Chief stares at the generator. After a while, he turns away.
The Chief turns back.
Master Chief is teleported away. Fades to black.
The following achievements can be unlocked on Two Betrayals across the Xbox 360 and Halo: The Master Chief Collection editions of Halo: Combat Evolved Anniversary. The original Xbox and PC and Macintosh releases of Halo: Combat Evolved did not contain achievement unlocks.
Two Betrayals was primarily designed by Bungie designer Dan Orzulak but it was eventually given to fellow designer Tyson Green. Two Betrayals shares most of its level geometry with Assault on the Control Room, albeit adding the phase pulse generator rooms and skipping the opening section of Assault on the Control Room: from where Echo 419 deploys John-117 to where he first finds members of Fireteam Zulu.
In an early story draft, John-117 returned to the Control Room to find Cortana had gone mad with power and now wanted to take over the universe. This plot point was cut for unspecified reasons. Cortana says British phrases like 'sod off' and 'toady about' in the opening cinematic of the level, because Jason Jones originally wanted Cortana to have a British accent. Cortana's voice actress Jen Taylor had already recorded the lines in her natural American accent when Joseph Staten raised the issue to Audio Director Martin O'Donnell. The dialogue and American accent were kept in the final release due to time constraints. In Halo: The Flood, Cortana says "piss off" rather than "sod off".
343 Guilty Spark's dialogue "Last time you asked me if it were my choice, would I do it?" was a mystery for 12 years until the release of the novel Halo: Silentium, which reveals that 343 Guilty Spark was referring to a question asked by the IsoDidact before 343 Guilty Spark was assigned to Installation 04, which was: "Tell me Chakas, if it was your choice, after all we have seen and survived... would you fire the rings?" This revelation provides context for many of 343 Guilty Spark's cryptic comments to John-117, in which he addresses the Master Chief as if they had met before and presumes the Spartan to be fully aware of protocol; it can be inferred that Spark somehow believed John to be the IsoDidact.
The events of this level occurs concurrently with the Halo: Fireteam Raven level Ice Canyon, which at one point takes place at the canyon where John-117 finds the Banshee to reach the final phase pulse generator. John-117 makes a brief cameo on Ice Canyon, in which he uses an M90 shotgun to kill a Flood tank form that was charging at Fireteam Raven. He then nods at the ODSTs before leaving them.
Halo: Combat Evolved
Halo: Combat Evolved Anniversary