fleeing the Covenant, the UNSC ship Pillar of Autumn stumbled upon one of these ringworlds, Installation 04. Against the wishes of the ring's artificial intelligence (AI) caretaker, 343 Guilty Spark, the human supersoldier Master Chief destroyed the ring to stop the threat from Halo and the Flood. The Covenant, unaware of the destructive nature of the rings, attempt to fire another ring, Installation 05, during Halo 2 in order to fulfill their religious prophecy. One race in the Covenant, the Elites, learn the truth about the rings, and join forces with humanity in order to stop the installation's firing. Though they are successful, the unexpected shutdown triggers a fail-safe protocol, priming all the rings for firing from one location, referred to as the Ark. Still oblivious to the true nature of the rings, the Covenant High Prophet of Truth and the remaining loyalist Covenant proceed to head to Earth, where they believe the Ark is buried. Halo 3s protagonist is Master Chief Petty Officer John-117, an enhanced supersoldier known as a "Spartan". Master Chief fights alongside the Arbiter, a disgraced Covenant Elite commander. Two other Elite characters, N'tho 'Sraom and Usze 'Taham, appear as the third and fourth players in cooperative play. Supporting characters from previous games return, including human soldiers Avery Johnson and Miranda Keyes. Also playing a role in the story is the Flood leader known as the "Gravemind". In Halo 2, the Gravemind escapes from confinement, invades the Covenant mobile capital city of High Charity, and captures the human AI Cortana. Plot After the events of the comic tie-in Halo: Uprising, the Master Chief arrives on Earth in east Africa, where he is found by Johnson and the Arbiter. The Chief and company return to a UNSC outpost where Keyes and Lord Hood plan a final effort to stop the Covenant leader, the High Prophet of Truth, from activating a Forerunner artifact the Covenant have excavated. The Chief clears anti-air Covenant defenses so Hood can lead the last of Earth's ships against the Prophet, but Truth activates the buried artifact, creating a slipspace portal which he and his followers enter. A Flood-infested ship crash-lands nearby; Elite forces arrive and vitrify the Flood-infected areas of Earth, stopping the threat. Following a message Cortana left aboard the Flood ship, the Chief, Arbiter, Elites, Johnson, Keyes and their troops follow Truth through the portal. Joining them is 343 Guilty Spark,