Considered by many to be the most powerful artificial intelligence ever created by humanity, Cortana was paired with the Master Chief in a last ditch effort by the UNSC to end the war with the Covenant. But as the military stronghold of Reach fell, the Chief and Cortana fled, eventually finding Halo and unlocking its secrets, an event which would lead them to the Ark. With all sentient life endangered by the Covenant, the Flood, and the Halo Array, the Master Chief and Cortana destroyed the Ark, bringing the conflict to an end. In the process, both were somehow brought to the threshold of Requiem, an ominously powerful Forerunner world with a dark secret. Cortana, now perilously beyond her operational lifespan, teeters on the brink of rampancy as this new world’s threat is finally revealed.