What's it about? U.S. Marshal Teddy Daniels (Leonardo diCaprio) arrives at the titular island and home to the criminally insane to investigate the inexplicable disappearance of one of its patients. As the probe deepens and he uncovers sinister practices, it is revealed that the agent has ulterior motives for his visit - to track down Andrew Laeddis, the arsonist who killed his wife.How does it end? With the revelation that Daniels is in fact Laeddis, and that his "arrival" at the island and subsequent investigation was a role play arranged by his doctors in order to come to terms with the fact that he murdered his wife after she'd drowned their children. At first appearing to understand, the film ends with him reverting back to the Laeddis persona and being taken away for a lobotomy. Why was it controversial? A lot of people read a degree of ambiguity into the ending which isn't really there - the twist reveal in which Daniels is shown to be Laeddis is clear cut, something which is even more self-evident on a second viewing. Perhaps more ambiguous is the degree of madness in his character, particularly in light of his last line, "which would be worse to live as a monster, or to die as a good man?" implying that he may be faking his relapse. There's a place for interpretation here, and the idea that perhaps he has a flash of realisation that he is actually insane and welcomes his lobotomy ends Shutter Island on its most satisfying note.