New-forged sons of the primarch Roboute Guilliman, the Primaris Ultramarines are peerless warriors whose sworn duty is to protect mankind from the predations of the xenos and the foul traitors of the Heretic Astartes. In a galaxy riven by eternal war, they and the other armies of the Imperium are all that stand between mankind and damnation. Their ship damaged by warp storms, the Ultramarines of Strike Force Cassian make for Kalides Prime. Here they hope to find safe harbour to repair their craft before rejoining the Indomitus Crusade. Instead, the Primaris Space Marines discover a world reduced to rot and ruin by the plague-ridden warriors of the Death Guard.