Vespertine by Margaret Rogerson

The dead of Loraille do not rest.

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 spirits with a ravenous hunger for the living. She would rather deal with the dead than the living, who trade whispers about her scarred hands and troubled past.

When her convent is attacked by possessed soldiers, Artemisia defends it by awakening an ancient spirit bound to a saint’s relic. It is a revenant, a malevolent being that threatens to possess her the moment she drops her guard. Wielding its extraordinary power almost consumes her—but death has come to Loraille, and only a vespertine, a priestess trained to wield a high relic, has any chance of stopping it. With all knowledge of vespertines lost to time, Artemisia turns to the last remaining expert for help: the revenant itself.

As she unravels a sinister mystery of saints, secrets, and dark magic, her bond with the revenant grows. And when a hidden evil begins to surface, she discovers that facing this enemy might require her to betray everything she has been taught to believe—if the revenant doesn’t betray her first.