Covenant forces arrived at Reach and obliterated Earth's last major military stronghold. The battered cruiser, the Pillar of Autumn, fled the devastation, carrying with it the sole surviving SPARTAN. The SPARTANs—an elite unit of supercommandoes, equipped with the fearsome MJOLNIR assault armor—were created as the ultimate soldiers.
Now, only one SPARTAN remains to carry the fight to the enemy. In accordance with the Cole Protocol, Captain Jacob Keyes—the Autumn's commanding officer—plotted a random, long-distance jump, hoping to lure the Covenant fleet away from Earth.
After deactivating the drive, the Autumn dropped into a distant, uncharted system. There was a Covenant fleet in the system as well, near a planet-sized ring-shaped construct, "Halo."