The problem with the book was hammered home for me when, after completing it, I immediately reread the prologue, which convinced me that Lehane lost his way with the ending. It’s a pity that screenwriter Laeta Kalogridis and Scorsese couldn’t come up with a different way to finish off the film.

Set in 1954 on a fictional island outside of Boston Harbor, it’s the tale of federal marshals Teddy Daniels (Leonardo DiCaprio) and Chuck Aule (Mark Ruffalo), who are assigned to go to the island’s one-of-a-kind hospital for the criminally insane — which, they’re told, houses “the most dangerous, damaged patients” — to search for a woman who has not only escaped from her escape-proof cell, but disappeared.

That’s the whole set-up and, indeed, the whole story. But then the film turns into a series of personality studies, focusing mostly on Teddy (who has plenty of interior demons), Chuck (who seems to be close to invisible even while we’re looking right at him) and Ben Kingsley as head honcho Dr. Cawley (a man of mystery and more than a hint of a sinister edge).

The dilemma introduced by the patient’s escape is compounded by Mother Nature in the form of a hurricane that wraps its winds and rains around the small island. Things get worse due to the resulting communication breakdown between Shutter and the mainland, as this all takes place four decades before cell phones were everyday tools.

It’s when those things get worse that Scorsese starts to make it all interesting. In revealing the internal makeup of Teddy, he gives us a wide spectrum of flashbacks. There are surreal, haunting images of his marriage to Dolores (Michelle Williams), who’s now gone but keeps reappearing as his voice of conscience; and horrific ones lingering in his memories of being a soldier and taking part in the liberation of Dachau.

The story keeps asking us if this federal agent is in good enough mental shape to be working in a place that’s filled with people in very bad mental shape.

Scorsese is aided by some outstanding production design from his regular collaborator Dante Ferretti (The Aviator, Gangs of New York), whose sets run from Dr. Cawley’s ridiculously lush living accommodations to the really creepy labyrinthine hallways and staircases in the hospital’s infamous Ward C. Oddly, Scorsese also makes use of some good old-fashioned rear screen projection, perhaps to better capture the flavor of the film’s ’50s timeframe.

As always, he gets some of the best actors around. There’s no point in discussing DiCaprio, beyond saying he’s once again terrific (although he drifts in and out of a Boston accent; the only one who nails it here is John Carroll Lynch as Deputy Warden McPherson). Other great but brief performances come from Robin Bartlett as a shaky patient named Mrs. Kearns, and Patricia Clarkson, who will only be revealed here as a woman in a cave. For the record, the actor playing the sinister Andrew Laeddis is not, as some people have hinted, Robert De Niro. He’s the brilliant and underappreciated Elias Koteas.

All kinds of dark secrets about the mental health profession start to take center stage, as does a descent into paranoia. There’s riveting stuff everywhere you look. Too bad the ending isn’t more concrete.