It's 1954, and up-and-coming U.S. marshal Teddy Daniels is assigned to investigate the disappearance of a patient from Boston's Shutter Island Ashecliffe Hospital. He's been pushing for an assignment on the island for personal reasons, but before long he wonders whether he hasn't been brought there as part of a twisted plot by hospital doctors whose radical treatments range from unethical to illegal to downright sinister.