by the mysterious Forerunners. The Covenant call this relic Halo, and believe it is a means of transcendence. The UNSC discover that Halo destroys all sentient life in the galaxy to prevent the parasitic Flood from spreading beyond Halo. The SPARTAN Master Chief and his artificial intelligence companion, Cortana, detonate the Pillar of Autumns engines, destroying Halo. Escaping the destruction via a fighter, the Chief and Cortana believe themselves the only survivors of the catastrophe. Plot The novel begins in orbit above planet Reach, as humanity fights the Covenant invasion forces. The last line of defence for the planet is an array of magnetic accelerator cannons (MACs) orbiting the planet. The Master Chief sends a team of Spartans to the surface of Reach to protect the MAC's planet-based power generators. Ultimately, the Covenant are able to destroy the generators and begin bombarding the planet's surface - melting its surface to glass ('glassing the planet'). The surviving Spartans flee underground to the hidden headquarters of the Office of Naval Intelligence. There they meet Dr. Halsey who, with help of some of the surviving Spartans, uncovers a strange crystalline shard in a cavern built by the ancient Forerunners. Pursued by the Covenant, the Spartans retrieve the shard and collapse the passage behind them, which saves them from the pursuing Covenant forces, but also traps them deep under the surface of Reach. The book then shifts to events occurring soon after Halo, as the Master Chief and Cortana drift through the ruins of Halo, they discover other survivors including Sergeant Johnson and Corporal Locklear. The group commandeer the Covenant flagship Ascendant Justice and use its slipspace capabilities to return to the Reach system. To prevent the Covenant from finding Earth with a tracking device, the humans plan to find a suitably undamaged human ship to take them to Earth. Upon arrival the group receive a radio signal used by the Spartans in their training days. On the surface, they find three Spartans and Vice Admiral Danforth Whitcomb, the Deputy Chief of Naval Operations. The Vice Admiral arms a "Nova thermonuclear mine", a weapon that would destroy the planet. The Master Chief and his newly acquired team of Spartans then proceed to rescue Dr. Halsey and the other Spartans that were trapped under the surface of the planet. Meanwhile, Cortana, still aboard Ascendant Justice, learns that the Covenant already know the location of Earth