On a distant world of the Imperium, an agent of Rogal Dorn finds himself the prisoner of a Legion whose loyalties may be divided. Shackled and bound, the former Luna Wolf must fight a battle of wits with his captor, lest the course of the Horus Heresy take an unexpected turn. Will his very presence drive his erstwhile allies into the arms of the Warmaster, or will maintaining the status quo prevent another Legion from turning traitor? And just who is the mysterious Space Marine aiding him from the shadows?