Early 20th century. Polina arrives at a girls' boarding school on a mysterious island to find her sister who disappeared under strange circumstances. Polina&amp;#39;s investigation is complicated not only by conflicts with other girls and the imperious mentor Zakharova but also by a strange obsession that drives the girls mad, one after another. Polina needs to find out what happened to her sister without losing her mind in the process and get off the island which is sinking in the abyss of insanity.！