The Pillar of Autumn flees the planet Reach.
When the Covenant assaulted the planet of Reach, there was little Captain Jacob Keyes and the crew of the UNSC Pillar of Autumn could do to stop them. The Human colony would inevitably fall and the Covenant would do as they had always done—scorch the world’s surface until there was nothing left alive.
As a veteran of the war, Keyes recognized that if the Covenant ever captured the Autumn and extracted its shipboard AI, Cortana, the enemy would have access to everything humanity had worked to keep safe, including the location of Earth. For this reason, he salvaged the last vestige of the SPARTAN-II project, a legendary super-soldier known as the Master Chief, and escaped into the darkness of Slipspace.
Upon emerging, the crew of the Autumn discovered that not only had the Covenant followed them, but also they had arrived near something no human had ever seen before. Against the black of space hung a mysterious ringworld installation, a place they would later come to know as Halo.