 When a suburban couple is brutally slaughtered one night by a hideous creature, police are unable to solve the horrendous crime. The couple s two young children, who were found unharmed, are removed from the home. Teri, the four-year-old daughter, is put up for adoption, while eight-year-old Alex, who has apparently been traumatized by the experience, is now completely catatonic. Alex is placed in Briarcliff Psychiatric Hospital for treatment. Nineteen years later, Teri is summoned to the bedside of her adoptive mother. Heavily medicated, the dying woman mumbles incoherently about Teri s "brother" and the "horrible thing" that happened. Teri is confused and puzzled, unaware of the past events or that she is adopted. But she soon discovers the truth that her real parents were murdered and the brother she never knew is now in a mental institution. Teri and her boyfriend, Chris, go to Briarcliff to finally confront Teri s past. They quickly discover that the crumbling institution is being closed down and all the patents are being moved to other facilities. Alex is one of the few who still remains. He has been catatonic and unresponsive all these years. But when Teri arrives and he senses her presence horrifying events begin to unfold. Patients and others begin to die horribly grotesque deaths as the creature is mysteriously unleashed in the dark corridors. Detective Nick Walenchky, who was a patrol officer when he handled the crime scene investigation into the killing of Teri s parents years before, is dispatched to investigate. When Briarcliff s security system inexplicably malfunctions and the power cuts off, the building becomes sealed tight. No one can get in or out. Teri, Chris and Nick join together with Derek, a tough orderly, and Diane, the sharp-tongued hospital administrator, in an attempt to resolve the crisis. It is soon discovered that Alex has vanished from his locked room and events quickly escalate in a night of terror. As each of those remaining inside are brutally attacked and killed by the elusive, shape-shifting creature, Teri must come to face a horrible reality; her own brother actually is the evil monster. And, if she is his flesh-and-blood could she be a monster too?