2552. Having barely escaped the final battle for Reach against the vast alien alliance known as the Covenant, the crew of the Pillar of Autumn, including Spartan John-117—the Master Chief—and his AI companion Cortana, is forced to make a desperate escape into slipspace. But their destination brings them to an ancient mystery and an even greater struggle. In this far-flung corner of the universe floats a magnificently massive, artificial ringworld. The crew’s only hope of survival is to crash-land on its surface and take the battle opposing the Covenant to the ground.