The Middle Ages. Finally, the Black Plague has passed, and for a while it seems evil has been defeated. Europe recovers; prosperity returns, trade resumes, and people slowly recover from the effects of the plague. Then, just as the Church relaxes its guard, war spreads across Europe. Widespread heresies challenge the authority of the Church. Revolts and rebellions threaten to topple the established monarchies and overturn the social order of Europe. And then the plague returns, worse than ever.

Thomas Neville, a neurotic warrior-priest, eventually discovers the cause. The minions of the Devil have been scattered throughout European society during the confusion of the Black Death. His task is to discover the identities of these shapeshifters so that the Church can move against them--but it is dangerous. These are master shapeshifters, perfect at their craft, and Neville can never be certain of whom he should trust.