For too long the Emperors Children have been denied their birthright. Their once-glorious Legion has been fractured into disparate warbands, condemned to ravage world after futile world in the pursuit of ambition and excess. But no longer.

Lord Fulgrim ascended Primarch of the III Legion, the Perfect Son, the Emperor-in-Waiting has issued a challenge to his scattered warriors: vanquish the Imperial world of Crucible, and bring him the head of the Black Templar charged with its defence.

But Fulgrims plans go far beyond the conquest of a single planet, and what should have been a swift and bloody offensive turns into a gruelling siege. With success uncertain, a world in flames around them, and the Legion turning their weapons inwards as well as out, the would-be champions are forced to confront a bitter truth. What must they sacrifice for victory and the favour of their Primarch, and what will be left of them when the war is over?