For millennia, the Adeptus Custodes remained true to their oath to defend holy Terra and the God-Emperor until their last breath. But when the Great Rift tears the Imperium apart, unleashing a host of demons upon humanity, they are faced with a dilemma. Should they continue to guard the Palace and the Golden Throne or once again travel to the stars to root out the very threat of the Ultimate Enemy? When Shield Captain Cartovandis receives a mysterious distress signal from the planet Vorgantian, he assembles a team of Custodians to investigate. Arriving on the planet, they find Vorgantian in a state of self-destruction, overrun by Chaos cultists. In a race against time, the Custodians must figure out what happened and hunt down those responsible before the madness reaches its true goal - something that lies in the hearts of the Custodians themselves.