Early 20th century. Polina arrives at a girls boarding school on a mysterious island to find her sister who disappeared under strange circumstances. Polinas investigation is complicated not only conflicts with other girls and the imperious mentor Zakharova but also a strange obsession that drives the girls mad, one after another. Polina needs to find out what happened to her sister without losing her mind in the process and get off the island which is sinking in the a of insanity.