Martin Scorsese's Shutter Island is a bucket of artisanal popcorn, an expertly made snack of kernels culled from the cobs of Alfred Hitchcock and M. Night Shyamalan.

Set in 1954 on an island off Boston, the film follows the investigation of U.S. Marshals Teddy Daniels (Leonardo DiCaprio) and Chuck Aule (Mark Ruffalo) into the disappearance of a patient from the fortress hospital for the criminally insane.

Atmospherically, this psycho-thriller adapted from Dennis Lehane's 2003 novel makes a case that insanity is catching. On Shutter Island, lights flicker, pipes drip, the iron bars in the cellblocks make ominous music. The sounds are underscored - and occasionally overscored, if there is such a thing - by chilling, dissonant passages from composers John Cage and John Adams, completing the effect.

Onto this haunted island storms Teddy, himself haunted by the horrors witnessed when he liberated Dachau, horrors compounded by the trauma of his wife's recent death in an apartment fire.

Teddy sees crazy people. For him, as for the movie audience, it's hard to distinguish insane from sane, prisoner from patient.

From the maniacal grins of shackled inmates to the enigmatic smiles of doctors (Ben Kingsley and Max von Sydow), everything Teddy sees triggers a disturbing memory. Still, he soldiers on, scouring the island for the escapee, Rachel, who killed her three children.

Teddy is tightly wrapped. And the overlong (2 hours, 18 minutes) film can't wait until he starts coming apart at the seams.

DiCaprio, the vertical furrow bisecting his brows growing deeper as the movie progresses, looks to be compensating for the shallow material.

There are many many fine performers here, including the terrific Patricia Clarkson as the elusive Rachel. But Shutter Island is not so much a character study as it is an atmospheric thriller.

Yes, it briefly considers medical and political issues topical in 1954. Namely: Is it better to lobotomize or medicate the insane? What's the difference between healthy skepticism and unhealthy paranoia? But these are tactical diversions, for Shutter Island is principally an exercise in mood and style.

Working with gifted cinematographer Robert Richardson and visionary production designer Dante Ferretti, Scorsese maximizes the creep-out factor of every tempest-tossed inch of Shutter Island, where Teddy's inner demons become externalized in geology and flesh.

Fallen branches from trees crack underfoot like broken bones. The island's jagged, slippery schist suggests the craggy, shifty characters who live there. The dead haunt the living.

And dead directors, especially Hitchcock, haunt the living Scorsese, an original who here makes an unapologetically derivative film full of visual nods that appeal mostly to movie geeks.

Most obviously, Shutter Island has a shower scene like Psycho, a haunted-stairway scene like Vertigo, tweedy shrinks sipping brandy as in Spellbound, and a rock-climbing cliffhanger like North by Northwest. Grad-level geeks will also recognize the references to Sam Fuller's Shock Corridor, Vincente Minnelli's The Cobweb, and Val Lewton's Isle of the Dead.

I enjoyed the visuals, including the backgrounds that looked deliberately faked, like Hitchcock's, and the ambiguous ending that will launch a thousand debates. In the Scorsese filmography, Shutter Island is but a middling destination.EndText