Heresy spreads throughout the galaxy and confusion reigns everywhere, and only one thing is certain: in the end, Horus and his legions of traitors will strike Terra. But it will not pass to her without a fight - it is surrounded by the Flaming Reef, a ring of guns and asteroid bases, just one of many similar defenses. Captain Arcadia of the Ultramarines finds himself among his war brothers, and the fleet of the apostate Master of War begins the final assault on the Throne World. Will he fight to the end, even in the face of imminent doom, or will his loyalty falter at the last moment?