THE lunatics are taking over the asylum, or that’s what Martin Scorsese’s impeccably crafted psychological thriller would have us believe.

But then perception and reality are completely blurred in this 1950s-set mystery, adapted by screenwriter Laeta Kalogridis from the best-seller by Dennis Lehane (Mystic River, Gone Baby Gone).

In many ways, Shutter Island is an odd fit for Scorsese, who has always punched low and hard on the mean streets of his beloved New York.

Here, he is all at sea on the Boston Harbor Islands, concealing some obvious sleights of hand with the plot behind directorial brio.

The production design is flawless, evoking moods and fashions of the era, and cinematographer Robert Richardson, nominated for an Oscar this year for Inglourious Basterds, uses contrasting colour palettes to good effect.

However, for all its style, Shutter Island is a largely predictable and pedestrian yarn, elevated by a superior cast. Even a consummate filmmaker as gifted as Scorsese undoubtedly is cannot polish mediocrity to a golden lustre.

US Marshal Teddy Daniels (Leonardo DiCaprio) and his new partner Chuck Aule (Mark Ruffalo) make the stomach-churning journey by water to Ashecliffe Hospital for the Criminally Insane with a hurricane closing in on the island.

Dr Cawley (Ben Kingsley), who oversees the facility, reveals that one of the patients (Emily Mortimer) has escaped and no-one has any idea how she could have disappeared without trace.

Examining the cell, Teddy discovers a scrap of paper bearing the scribbled words: “The law of 4. Who is 67?”

It's the first of many mysteries.

As the cops interview the staff, including the threatening Dr Naehring (Max von Sydow), Teddy and Chuck begin to sense something is terribly awry on Shutter Island.

As paranoia grips the men, Teddy becomes convinced that Cawley and his security team are secretly holding an additional patient hostage somewhere within the hospital’s crumbling walls. Alas, voicing his fears would make the cop sound just as mad as some of the inmates.

Shutter Island is arguably Scorsese’s most mainstream film, and with more than $100m at the American box office and counting, it may well be his most commercially successful.

However, it is not his finest offering by a long way, leaving us disoriented but ultimately unfulfilled as the cops get their answers.

DiCaprio’s uneven and unconvincing performance makes sense in retrospect, as do the clumsy special effects, but both prove distracting and stop us from feeling completely immersed in the story.