Halo: Nightfall tells the personal story of Jameson Locke, a legendary manhunter and agent with the Office of Naval Intelligence (ONI), Earth s most powerful and secretive military branch. He and his team are investigating terrorist chatter on the distant colony world of Sedra, when they are caught in a horrific biological attack. Led by Locke, ONI agents are forced to coordinate with Randall Aiken, a local commander with a remarkable history and deep-rooted mistrust of ONI. As they unravel a plot that draws them to an ancient, hellish artifact, they will be forced to fight for their survival, question everything, and ultimately choose between their loyalties and their lives.