After seven long years of conflict, the Horus Heresy nears its end. But now, as the Warmaster Horus marches on Terra to rip his father from the Throne, the seat of the arch-traitor’s power lies empty. Cthonia, a world once dominated by brutal murder-gangs, is occupied by the Emperor’s praetorians—the indomitable Imperial Fists. For the Sons of Horus, this outrage demands a reckoning.

After seven years of bitter war, the end has come at last for the conflict known infamously as the Horus Heresy. Terra now lies within the Warmaster’s sights, the Throneworld and the seat of his father’s rule. Horus’ desire is nothing less than the death of the Emperor of Mankind and the utter subjugation of the Imperium. He has become the ascendant vessel of Chaos and amassed a terrible army with which to enact his will and vengeance. But the way to the Throne will be hard as the primarch Rogal Dorn, the Praetorian and protector of Terra, marshals the defences.

The Horus Heresy is a civil war on a scale the likes of which the galaxy has never seen before. After the Great Crusade united the disparate worlds of humanity, the very warriors who made it possible turned on each other and tore it apart. Soon after word reached Terra of Horus's nascent rebellion, Mars fell. Set upon by the forces of the Alpha Legion before they had even recovered from the Razing of Prospero, the Space Wolves have been hounded to the edge of the Alaxxes Nebula. In desperation, Leman Russ called out to his primarch brothers for aid. None came.

The Horus Heresy is a civil war on a scale the likes of which the galaxy has never seen before. After the Great Crusade united the disparate worlds of humanity, the very warriors who made it possible turned on each other and tore it apart. The Siege of Terra looms, and the fate of the galaxy balances on a razor's edge.

The daemon prince Mortarion has emerged from the Eye of Terror at the head of a vast plague-horde, intent upon the corruption of the Imperium he once served. Under Supreme Grand Master Geronitan, the Grey Knights finally meet the daemon army in battle on the plains of Kornovin - a mobilisation of the Chapter the likes of which few have ever seen. Kaldor Draigo and his fellow brotherhood masters lead from the front, trusting to their lord's secretive plan...until Geronitan is unexpectedly struck down by the Death Lord.