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.

The Realm of Beasts has ever been a place of savagery and destruction, defiant in the face of Sigmar's feeble attempts at liberation. But now, deep within the mountains of the Ghurish Heartlands, something ancient stirs. A god long-trapped is about to awaken, and the drumbeat of war calls. Ferocious Ironjawz, gluttonous Ogors and towering gargants all set their sights on the human interlopers, determined to cast down their keeps.

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 Blood Angels Chapter of Space Marines is under threat. Having obliterated all human life in the Red Scar region of space, the largest tendril of Hivefleet Leviathan ever seen in the Imperium has converged and is making relentlessly for Baal. To face this awesome foe, Commander Dante has called upon the Successor Chapters of the ancient Ninth Legion. The Sons of Sanguinius gather in numbers not seen since the dark days of the Horus Heresy.

Horus has rebelled against the Emperor by purging his and his brother's Legions, but what was supposed to be a secret act of murder has been revealed. In the Emperor's name, Rogal Dorn and Malcador the Sigillite dispatch the largest force of legionaries and primarchs ever assembled to end Horus' rebellion before it can begin. But the loyalists, on their way to enact vengeance, do not know the depth of the betrayal they face. They will not be the perpetrators of a massacre, but its victims.