The main character, Polina, arrives at a reformatory boarding school for headstrong young ladies with a secret mission—to investigate her sister’s disappearance. She must confront a harsh mentor, the other students, and, ultimately, a strange obsession driving the local girls mad. The school’s rehabilitation program has the opposite effect: the heroines succumb to temptation and surrender their souls to the devil. Repressed passions and dangerous relationships within the walls of this “model” institution awaken an ancient evil.