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.

For Ianthe, war is all too familiar. A former soldier in the Astra Militarum, she now serves Inquisitor Covenant as an agent of the Throne. Her first mission sees her investigating a cult called the Children of Eternity. Falling foul of the local Enforcers, Ianthe soon learns that war in the shadows is seldom straightforward and that the local, angry law-keepers are the least of her troubles.

In the Pandorax System, on the death world of Pythos, an ancient secret that has laid buried for millennia. Ignorant of this terror, troopers of the Catachan 183rd, stranded on Pythos, find themselves under attack by the forces of Chaos. Daemons in their thousands flock the sky, and none other than Warmaster Abaddon leads the attack. With the Death Guard and Black Legion arrayed against them, the Catachans appear to be doomed, until salvation arrives in the form of the entire Dark Angels Chapter. But what is the so-called 'Damnation Cache'?

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.

On the 13th day of Secundus, the bombardment of Terra began. With the solar defences overcome through the devastating strength of the Traitor armada and the power of the warp, Horus launches his assault on the Throneworld in earnest. After withstanding a ferocious barrage of ordnance, an immense ground war commences outside the Palace, with every inch gained paid for in the lives of billions.