Shutter Island Spoiler

At first glance, the 2010 movie stars Leonardo Di Caprio as U.S. Marshal Teddy Daniels 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. 

Teddy's investigating skills soon provide a promising lead, but the hospital refuses him access to records he suspects would break the case wide open. As a hurricane cuts off communication with the mainland, more dangerous criminals "escape" in the confusion, and the puzzling, improbable clues multiply, Teddy begins to doubt everything - his memory, his partner, even his own sanity.

But what we find out is that Teddy is a World War II veteran and coming back from the war in which he became the maintenance man at his own apartment building and he was never really a U.S. Marshal. He was married to Dolores Chanal, but has no children and he is a pyromaniac who burnt down his own apartment, killing four people - one of which was his wife. He also thought to have made up the conspiracy that there is a twisted plot as to why he's at Shutter Island's hospital.

In his extreme mental distress at learning that his fire killed his wife, he broke down and disso­ciated himself from reality. He created a new history. In this new history, a hideous man named Andrew Laeddis (really a reflection of the ugly and unbearable side of himself) was the man who “lit the match that caused the fire, that killed his wife.” Andrew Laeddis was sent to Shutter Island. To explain his own exis­tence on Shutter Island, Teddy Daniels remade himself as a U.S. Marshal, orig­i­nally sent here to hunt down Andrew Laeddis.

In reality, the newly incar­cerated Teddy Daniels was declared insane and was sent to Shutter Island. At Shutter Island, Teddy became the subject of an exper­iment. The exper­iment was one in which the psychi­a­trists would attempt to implant false memories into Teddy’s mind. Teddy, in a state of delusion, claimed that he was a U.S. Marshal to justify his presence. He met Dr Cawley who invented Rachel Solando for him to hunt down. Dr Sheehan, posing as Teddy’s fellow Marshal and partner Chuck, stays close to him to push him in the right direction. He encourages Teddy to continue the hunt (“I've never quit anything”); instills paranoid fear in him (the mausoleum scene); and plays upon that paranoia (urging him not to go to the light­house in an exercise in reverse psychology), all in an attempt to ensure that he reaches the light­house (in a highly unstable state) for the final event.

When Teddy reaches the light­house, he is confronted by the incon­sis­tencies and flawed logic of every­thing that he has been going through. He is presented with a far more reasonable expla­nation, though it is a fabri­cated one. This is the point at which the exper­iment is judged to have either failed or succeeded. If Teddy accepts this ficti­tious account, the psychi­a­trists have succeeded in attempting to implant a false memory into a patient.

Teddy has been through this before, and he now realizes that there is no way out of Shutter Island. He tells the doctors that he accepts their narrative in order to avoid lobotomy. However, sitting on the steps outside, he recon­siders and decides that lobotomy would be better than chasing Andrew Laeddis for the rest of his life: he figures they’ll just try to keep forcing this lake house narrative on him over and over again. When asking whether it’d be “better to live as a monster or die a good man,” Teddy is making a choice to take the lobotomy and thus die a good man. He refuses to accept the reality that he is just a main­te­nance man whose wife died because of his pyro­mania, and is instead perpet­ually stuck in a delusion in which he is Teddy Daniels, U.S. Marshal hunting down Andrew Laeddis (an entity created in his disso­ciative disorder), the man who killed his wife.