An agent of Rogal Dorn on a distant planet of the Imperium finds himself captured by the Legion, which may be split along the lines of allegiance. Chained and imprisoned, the former Luna Wolf must face his captor in a battle of wits to prevent the Horus Heresy from taking an unexpected turn. Will he push his former allies into the arms of the Warmaster with his very presence, or will maintaining the current state of affairs prevent another Legion from betraying him? And who is the mysterious space marine who is secretly helping him?