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. Spark sends Sentinels to take the Spartan's head, and the AI inside his helmet. After destroying the Sentinels in the Control Room, Cortana tells the Chief to destroy three Phase Pulse Generators to buy some time, in case the Monitor finds a way to activate Halo without the index. While Cortana tries to locate the Pillar of Autumn's crash site, the Master Chief must hijack a Covenant Banshee and set out to destroy the generators. After destroying the third pulse generator, Cortana teleports the Master Chief to a Covenant cruiser: The Truth and Reconciliation where the level Keyes begins.