For millennia, the Adeptus Custodes remained faithful to their duty—to protect the sacred Terra and the God-Emperor. But when the Great Rift tore the Imperium apart and unleashed hordes of demons upon humanity, they face a dilemma. Should they continue guarding the Palace and the Golden Throne, or travel to the stars to eradicate the Absolute Evil? When shield-captain Cartovandis receives a mysterious distress signal from the planet Vorgantians, he assembles a team of Custodians to investigate. Upon arrival, they find a world locked in self-destruction—seized by Chaos cultists. In a race against time, the Custodians must determine what happened and track down the guilty before madness reaches its true aim—something that lies in the hearts of the Custodians themselves.