On the planet of Molech, the Titan Legions go to war against the armies of Horus.

Once the favoured son of the Emperor of Mankind, the name of Horus has become a curse to the loyal defenders of the Imperium, and a rallying call to the traitor forces tearing across the galaxy. While their allies wage war on a thousand different fronts, the XVIth Legion descend upon the Knight World of Molech - home to House Devine and their feudal levies, and a principal seat of Imperial military power. Just what could have drawn Horus to attack such a strongly defended planet, and what might he be willing to sacrifice to fulfill his own dark destiny?