Teddy, a U.S. Marshal, is investigating the disappearance of a patient from a locked room at a psychiatric facility located on Shutter Island. It is revealed that the patient's story was fabricated to test Teddy, as he is actually a patient who is living in a fantasy world where he is still a marshal. In reality, Teddy's wife killed their children, which drove him insane. The film is a psychological thriller that uses lighting, sound effects, and editing to build suspense and mystery around the secrets of Shutter Island.