With the solar defences overcome by the Traitor armada and the power of the warp, Horus launches his assault on the Throneworld. After a ferocious barrage of ordnance, an immense ground war commences outside the Palace with every inch paid for with countless lives. The front lines are beyond horrific, the very air reduced to poison and blood. The outer redoubts cannot possibly hold long, even with the loyal primarchs to reinforce them, for Horus has his own generals. Between the plague weapons of Mortarion and the fury of Angron, the defenders face a losing battle.