Raid on Ivanoff Station
- "You are a fool. Even now, your kind tinkers with the Composer in the shadow of the third ring. Children and fire, who disregard the welfare of the galaxy."
- — The Didact
- Main article: Battle of Requiem
The Didact, an ancient Promethean general, had been released from imprisonment on Requiem and planned to use a device known as the Composer to digitize humanity, preventing them from threatening Forerunner dominance. With Captain Del Rio of the UNSC Infinity dismissing this threat and having the ship leave Requiem, Master Chief John-117 was left to pursue the Didact alone with his increasingly rampant AI, Cortana. The Master Chief's attempts to stop the Didact from leaving Requiem were unsuccessful, however, and the Promethean escaped aboard his flagship, Mantle's Approach. However, John-117 and Cortana stowed away on one of the Covenant Lich deployment craft accompanying the Didact's ship as it entered slipspace, headed for the Composer's location.
Following the Didact through slipspace aboard a Covenant Litch, the Master Chief and Cortana were surprised to discover that the Didact had taken them to Installation 03, which Cortana recognized as the location where UNSC Infinity found the coordinates to Requiem. The two quickly realized that the Didact is not headed towards the Halo ring but rather the nearby Ivanoff Station. The Master Chief hijacked the Lich and contacted Doctor Sandra Tillson on the station, who was relieved to hear from friendly forces. Unfortunately, Cortana experienced an episode of rampancy, causing her to lose focus and crash the Lich into the station.
After regaining consciousness, the Master Chief contacted Tillson to begin evacuation procedures, but was warned that the Covenant have already taken over Ivanoff Station's landing bays. The Master Chief promised to do what he could to clear an evacuation route on his way to Tillson and made his way through the station. Arriving in Landing Bay 7, the Master Chief found the station's forces desperately defending it against an unending stream of Phantoms. Using the Harbormaster's control station, the Master Chief erected a shield that prevented more Covenant from entering and cleared the landing bay of enemy forces. Once the bay was clear, the Master Chief resumed fighting through the station as the Didact scanned it. Cortana realized that the Didact only knew that the Composer was on the station but not where it was and was thus looking for it. The Master Chief fought his way to the station's control room which was under attack by a pair of Hunters. The Master Chief killed the Hunters and entered an elevator to meet with Tillson.
Tillson started the elevator down and the Master Chief explained that the Forerunner artifact the Ivanoff had scientists excavated was a weapon that the Didact wanted back. Tillson warned the Master Chief that the Composer couldn't be moved, it having taken three months and "the biggest starship the UNSC could throw at it" to move the Composer to Ivanoff Station in the first place. Recognizing this, the Master Chief had Tillson give Cortana access to the station's supply manifests so they could find a way to destroy the Composer, denying the Didact his prize. Cortana located seven excavation-grade HAVOK tactical nuclear weapons in the station's manifest. Tillson initially protested using them to destroy the Composer due to the years of work the scientists had invested in studying it. When the Master Chief refused to relent, Tillson reluctantly agreed to have the nukes primed for remote detonation and to continue the evacuation.
The Master Chief made his way to the atrium where the Composer was stored only to be informed that the Covenant had shot down the station's first evac shuttle. Recognizing that the station had outer turrets, Cortana instructed the Master Chief to take her to the controls so she could reprogram the turrets to cover the station's evacuation. The Master Chief reentered the main structure of the station and resumed fighting through the various corridors, facing Covenant boarding parties at two sets of airlocks as the Didact kept scanning the station for the Composer. Finally, the Master Chief reached the control area and after eliminating the two cloaked Sangheili Zealots located there, inserted Cortana into the control systems. Cortana, despite her rampancy growing ever worse, was able to activate Ivanoff Station's Onager cannons and have them fire on the Covenant ships besieging the station. The Master Chief alerted Tillson who promised to issue the final evac orders and instructed him to meet her and her crew back on the upper platform where they would help the Master Chief get their nuke to the Composer.
Fighting his way back to the atrium, the Master Chief discovered that Covenant forces had found the Composer. To keep the Covenant from warning the Didact, the Master Chief took control of a nearby Mantis and engaged Covenant forces made up of Type-32 Ghosts, Type-26 Wraiths, Banshees, Phantoms and ground troops dropped by the Phantoms. During the fight, the Master Chief contacted Tillson for his nuke, but was warned that it was not ready yet. After multiple waves of enemies, the surviving Covenant forces retreated from the atrium. Unable to raise Tillson, the Master Chief made his way to a nearby elevator to find her. As the elevator took him higher into the station, the Didact finally located the Composer and used Mantle's Approach's tractor beam to remove it from the station, removing the roof of the atrium entirely and disrupting Cortana so much in her rampant state that the Master Chief had to help her focus again to get her to find Tillson.
Reaching Tillson, the Master Chief warned her that the Didact had the Composer and that she needed to evac her remaining people. The Master Chief inserted Cortana into the station's systems and ordered her to find something that could carry a payload. Noticing the Composer charging, the Master Chief asked Cortana to reactivate the station's defenses, but she was unable to. The Didact fired the Composer at the station, digitizing everyone aboard except the Master Chief who was rendered immune by the Librarian.
- Main article: New Phoenix Incident
Following the digitization of Ivanoff Station's personnel, the Master Chief was awoken to a traumatized Cortana and piles of ashes. The Master Chief told Cortana that more people would die if they failed to stop the Didact from reaching Earth with the Composer. Cortana was able to pull herself together and spin up one of the station's F-41 Broadswords located in Hanger C-11. Despite their losses, the Master Chief assured Cortana that the fight wasn't over yet. With the Broadsword armed with one of Ivanoff Station's HAVOK tactical nuclear weapons, the Master Chief followed the Didact through slipspace to Earth where he attempted to digitize the population of humanity's homeworld as he did Ivanoff Station. However, the Master Chief was able to board the Didact's ship, Mantle's Approach and destroy it and the Composer with the nuclear weapon he retrieved from Ivanoff Station, preventing the Didact from digitizing more than the population of New Phoenix.
A handful of the Ivanoff's personnel managed to escape into the nearby asteroid field and were later saved by search and rescue teams.
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