Martin Scorsese sets himself a near-insurmountable challenge with Shutter Island, an intense and often bleak psychological puzzle that, bar flashbacks to 1952 and the liberation of Dachau in 1945, plays out entirely in a mental asylum on a windswept island near Boston in 1954. The source novel by Dennis Lehane keeps its cards close to its chest for much of its telling, and the problem was always going to be how to keep a complicated shaggy-dog story with a B-movie edge going for more than two hours without sending an audience into the confused territory of no-return.

Two US Marshals, Teddy Daniels (Leonardo DiCaprio) and Chuck Aule (Mark Ruffalo), arrive at Ashecliffe hospital for the criminally insane on a boat that emerges from the fog in the shadow of a rocky, guarded island. They’re at Ashecliffe to investigate the disappearance of a patient, which takes strange turns from the off. Patients whisper weird things. One scribbles Teddy a note – ‘run’ – and there are question marks hanging over the validity of the vanished patient. Soon, Teddy starts to fear the motives of his hosts and they, in turn, appear wary of his presence on the island.

There are many fantastic scenes, from a vertiginous cliff-top sequence to a storm-lashed dash through the woods as trees fall around Teddy and Chuck. The problem is that, narratively, by the time the film reveals its hand way past the two-hour mark, turning the story on its head and causing us to question much of what we’ve seen before, it’s neither surprising nor smart enough to compensate for some of the film’s more frustrating episodes. Judged as a piece of mainstream narrative cinema, Shutter Island is flawed. Judged, however, as a big-budget experiment at getting inside the head of a disturbed character and channelling an entire film through that same mind, it’s a ballsy, impressive effort.