By Charles Bodsworth BBC News Online

Insomnia opens with startlingly white snowy expanses and an already fatigued-looking Al Pacino.

He plays Will Dormer, an Los Angeles cop sent to solve the murder of a 17-year-old girl in a small Alaskan town.

During the Alaskan summer, night barely falls and the midnight sun relentlessly illuminates every minute of Dormer's investigation.

Light seems to be everywhere in the film, a constant presence leaking into every scene.

Hilary Swank plays local cop Ellie Burr

Dormer barely sleeps as he tracks the killer, troubled not only by the unfamiliar light but also by what he has left behind in Los Angeles, where an investigation into his unorthodox policing methods is ongoing.

To make matters worse, his partner Hap (Martin Donovan) is planning to cut a deal with the investigators that could end Dormer's career.

Pacino's performance is as understated as ever.

His nagging concerns and sleeplessness become etched on his face and through subtle glances or movements we understand his anger and slowly deteriorating mental state.

As usual in this kind of thriller, the local plods are floundering before the arrival of the hard-boiled cop from the big city.

Pacino's character, like all the detectives we admire, is able to spot significance in the tiniest detail and looks like he will be a match for the murderer.

Robin Willliams' cannot match Pacino

But things begin to spiral out of Dormer's control after he sets up a trap for the killer, which leads to a thrilling chase through the thick lakeside fog.

From that point on the film really hits its stride, with the killer and Dormer locked in an increasingly desperate game of manipulation.

It would take a fine actor to match Pacino in this game, and Robin Williams as the murderer is not that actor.

He can do inspirational-but-wacky genius and wacky-and-inspirational rebel - that much we know. Well, we now also know he cannot do much more.

To his credit he manages a certain degree of slippery intelligence, but cannot muster the malevolence that would really make his character terrifying.

The director, Christopher Nolan, who previously directed the inventive Memento, compensates with assured control over the pace and tension of the film.

Will Dormer's self-assurance slowly deteriorates

The camera is always on Pacino's character as his self-assurance diminishes and we follow every turn of his psychological state.

Nolan has an eye for a good chase sequence, topping the earlier pursuit through the fog with one across a log jam in a lake, ending with Dormer falling and becoming trapped beneath the immovable logs.

Again the scene is illuminated by the intense Alaskan light which sears through the gaps in the logs as he frantically searches for an escape route.

It would be unfair to give too much away about the ending of the film, suffice to say that it pushes all the buttons we expect of a police thriller.

But the real strength of Insomnia is the way it combines what we expect of a cop film with an unexpected capacity to unsettle its audience and provoke their thoughts.

Insomnia is now showing across the UK..