Erasmus Crowl, Inquisitor of the Ordo Hereticus, faithfully and tirelessly serves in the unimaginably terrible city that occupies the entire surface of Terra, for even the Throne World is not protected from the machinations of the insidious enemies of humanity. While fulfilling his duties, Crowl becomes embroiled in a mysterious conspiracy, the threads of which stretch into the Imperial Palace itself. The investigation forces Erasmus to descend lower and lower into the dungeons of the sacred citadel and attracts the attention of many hidden forces. Crowl and his acolyte Spinoza find themselves hunted by heretics, xenos, servants of the dark gods, and perhaps even other inquisitors. They will soon learn a terrible truth that could threaten the existence of the entire Imperium.