It all starts when the Covenant, an alien race, sets their eyes on Earth.They are bent on whiping out the human race.An unexpected attack on Earth kills all but one of the genetically-engineered cyborg soldiers, known as SPARTAN-|| soldiers.Aboard The Pillar of Autumn, a small Halcyon - class warship, the last SPARTAN-|| soldier remains in a cryosleep chamber.In one last attemp to lead the Covenant away from earth the captain of the Pillar of Autumn, Jacob Keyes, is forced to land ont the ancient ring- world, Halo.