The isolated forge world of Diamantus faces a threat of apocalyptic proportions – a warped and mutated space hulk infested by the forces of Chaos, commanded by the monstrous datagnost Voldire, disciple of the dread demigod Vashtorr the Arkifane. As the battle-weary Carcharodons make their stand alongside the Adeptus Mechanicus, horrors and nightmares raining down around them, the Space Marines must confront their place within this new Imperium, and destroy the hulk before Diamantus is lost.