A holy harbinger of war from the Legio Metalica, the Imperator-class titan Casus Belli has served the Omnissiah for ten thousand years, routing armies and wiping out cities. As war engulfs the Dark Imperium, this mechanical god of battle arrives on the planet Nicomedua to destroy the armies of the renegades and tech-priests who have fallen into heresy. Leading a tactical team of Titans, Imperial Knights and Skitarii, Casus Belly must defeat corrupted war machines, traitorous legionnaires and hordes of cultists. As apocalyptic battles rage across the world, an equally deadly battle unfolds within the titan itself: Magos Exasa, commander of the Tech-Guards Casus Belli, must identify and stop his enemies before their insidious plans come to fruition.