When a suburban couple is brutally slaughtered one night by a hideous creature, police are unable to solve the horrendous crime. Teri, the four-year-old daughter, is put up for adoption, while her eight-year-old brother Alex, seemingly traumatized by the experience, is now completely catatonic and placed in Briarcliff Psychiatric Hospital for treatment. Nineteen years later, Teri's dying adoptive mother reveals the shocking truth about her parents' death and Alex's institutionalization at Briarcliff. Teri sets out to the institution to confront her past and finds Alex, who has been catatonic and unresponsive all these years. Yet when he senses Teri's presence in the hospital, horrifying events begin to unfold. It is soon discovered that Alex has vanished from his locked room, giving way to a night of complete terror. As those inside are brutally attacked and killed by the elusive, shape-shifting creature, Teri must come to face a horrible reality; her own brother is actually the evil monster. And, if she is his flesh-and-blood … could she be of the same evil?