In the midst of the post-war era, U.S. Marshal Teddy Daniels, a former World War II soldier, arrives at Ashecliffe Hospital on Shutter Island, a remote facility housing the most troubled and violent mental patients. His mission is to investigate the disappearance of a patient named Rachel Solando, who vanished during a transfer to another wing of the hospital. As Teddy delves deeper into the mystery, he becomes increasingly unsettled by the eerie atmosphere and the unsettling behaviors of the inmates. Teddy's own demons begin to surface as he struggles to reconcile his wartime experiences with the present reality. His obsession with finding Rachel grows, and he starts to question the motives of the hospital staff, particularly Dr. John Cawley, a charismatic and seemingly benevolent psychiatrist. As Teddy's investigation unfolds, he becomes convinced that someone is hiding something, but his own grip on reality begins to slip. The lines between fantasy and reality blur as Teddy's troubled visions and flashbacks intensify. He becomes increasingly paranoid, suspecting a sinister plot to conceal the truth about Rachel's disappearance. His fixation on solving the mystery leads him down a rabbit hole of paranoia and deceit, where nothing is as it seems. As the story unfolds, Teddy's true identity and purpose are slowly revealed, adding layers of complexity to an already tangled web of intrigue. The film builds towards a climactic finale that challenges the audience's perceptions of reality, leaving them questioning what they've just witnessed.