Incarcerated in a foreboding mental institution after an act of arson , Kristen (Amber Heard) has no memory of her life before the incident. As kindly psychiatrist Doctor Stringer (Jared Harris) attempts to unlock the secrets of her psyche, Kristen meets her fellow patients, including the self-assured Sarah (Danielle Panabaker) and unpredictable Emily (Mamie Gummer). While the misery of being confined to the sinister institution is quite enough, Kristen's stay gets considerably worse when a mysterious phantom-like figure begins picking off the girls. Can Kristen work out who is behind the killings before it's too late?