During the Great Crusade, it falls to the primarch Corax of the Raven Guard to humble the immense void-cities of the Carinae. Determined to bring these worlds into compliance, he unleashes the might of his Legion and a massive war host of the Imperial Army. But the lords of Carinae are well defended and without remorse. At the height of the conflict, at the void-city of Zenith, a dread bio-weapon from an ancient time is unleashed. At once, the Imperial force is brought to its knees, as allies are turned against each other and the Raven Guard left to face almost insurmountable odds. As the campaign teeters on the brink of failure, Corax's desire for vengeance is severely tested against the need for a swift and certain resolution to the war.