Eighteenth-century reclusive priory in the Smolensk Region. Local nuns and Joan, their prioress, are afflicted with demonic possession. A young exorcist, Father Suryn, arrives and attempts to save the nuns but to no avail. Soon, he struggles with spiritual dilemmas and feelings developed for Mother Joan. He promises to heal the nun even at the cost of eternal damnation. The film is inspired by a short story by Jarosław Iwaszkiewicz.