When her convent is attacked by possessed soldiers, Artemisia defends the Gray Sisters by awakening the revenant bound to a saint's relic, even though she runs the risk of being possessed permanently by the powerful ancient spirit.

Artemisia is training to be a Gray Sister, a nun who cleanses the bodies of the deceased so that their souls can pass on; otherwise, they will rise as twisted spirits with a ravenous hunger for the living. When her convent is attacked by possessed soldiers, Artemisia fights back by awakening an ancient spirit bound to a high saint's relic. It is a revenant, a malevolent being now whispering in her head. Wielding its extraordinary power almost consumes her in body and soul. But death has come to Loraille, and only a vespertine, a priestess trained to wield a high relic, has a chance of stopping it. Yet the age of vespertines has passed, their knowledge and training lost with time. As Artemisia investigates a mystery of saints, secrets, and dark magic, an ancient evil is stirring. Can an untrained girl, tormented by the burden of containing the revenant's devouring power, have any hope of defeating it?