Set in 2525, twenty-seven years before the events of Halo: Combat Evolved, the novel tells the story of the United Nations Space Command's first encounter with the alien collective known as the Covenant on the colony world of Harvest, and the beginning of the long war that follows. The novel is an ensemble piece, following human and alien characters. The protagonist is a young Marine, Staff Sergeant Avery Johnson, who also appears in the Halo video games.