U.S. Marshal Teddy Daniels arrives on Shutter island to investigate the disappearance of a murderess. The hospital hosts the criminally insane, isolating them in the middle of the Boston Bay. From the moment he arrives with his inexperienced new partner, he sees a conspiracy going on, realising that nothing is quite as it seems. As Dr. John Cawley, the head psychiatrist on the island, continually obfuscates, the Marshal tries to unravel the mystery of the prisoner's implausible escape and other weird occurrences on the island.