When the Heresy shattered the Imperium, the Primarch Corax and his Raven Guard barely managed to escape the trap Horus had set on Isstvan V. Attempting to heal the wounds inflicted on his Legion, Corax rushes to Terra to seek the aid of his father, the Emperor of Man. Having gained access to an ancient secret, Corax begins to rebuild the legion, plotting revenge on the traitors. But the ranks of the Raven Guard had already been infiltrated by the infiltrators of the most cunning and two-faced of the traitor primarchs, Alpharius. Corax's plans hang in the balance, and with them the future of the Galaxy. After all, if the secret of the creation of the Primarchs and Astartes falls into the hands of Horus, the massacre at Isstvan will seem like a trifle compared to the battles of the future.