When the game begins, Master Chief is back on a thoroughly conquered, Covenant-controlled Earth, and Cortana is still a prisoner of Gravemind. Covenant ships are hovering over an excavation site a few miles from the ruins of New Mombasa and have uncovered a large artifact in this site. The Arbiter, along with the remaining Elites, have allied themselves with the human forces after splitting from the rest of the Covenant in Halo 2.