The sun never sets on some parts of the world.

The 24-hour daylight north of the Arctic Circle keeps many strangers from sleeping – and is an unlikely setting for film noir. In his latest thriller, director Christopher Nolan (“Memento”) explores what happens when an intelligent person is forced to do important things while totally exhausted. The result is a fascinating, exciting and unconventional film.

The alien-looking glacial fields of northern Alaska roll across the screen to open the film. The rickety plane carrying legendary detective Will Dormer (Al Pacino) and his partner Hap Eckhart (Martin Donovan) enters the frame; inside, the LAPD homicide detectives discuss an investigation of their department. Later, Eckhart breaks the news that he plans to cut a deal with Internal Affairs, leaving Dormer vulnerable to the probe of one mysterious case.

Their mission in Alaska is to solve the murder of a teenage girl in the fictional town of Nightmute. They get a lead, track the killer, give chase and lose him in the fog. In the confusion, the fatigued Dormer shoots Eckhart dead.

Anyone who has worked through consecutive sunrises can empathize with Dormer in his insomnia. Pacino masterfully simulates the fatigue that can only stem from a consciousness marathon measured in hundreds of hours. With the simple slurring of one word or the stiff, plodding gait with which he walks straight up to the house of an armed killer, he embodies exhaustion.

The death of Dormer’s partner complicates his emotional involvement – with Eckhart out of the way and the evidence successfully doctored, he’s in the clear. Pacino expresses the battle of remorse and relief with wonderful restraint. By the end of the film, Dormer is no longer sure whether he shot Eckhart intentionally or simply mistook him for the murderer in the fog.

Robin Williams is surprisingly disgusting as the sociopathic Walter Finch, author of several detective novels, murderer of the girl and sole witness to the Eckhart shooting. Finch’s manipulation of Dormer follows a classic villain format: “I’ve got leverage on you” segues into, “We’re not so different.” It isn’t hard for someone sympathetic with Dormer to cling to Finch’s claim that it is easy to kill someone.

A wrench finds its way into the works in the form of the young, brilliant and overlooked Detective Ellie Burr (Hilary Swank). Assigned to the apparently open-and-shut Eckhart investigation, Burr unfolds the truth and topples her own idol. Swank excels at conveying Burr’s energy, determination and sharp wit, as well as her bewilderment at the revelation of Dormer as fallible.

“Insomnia” is not merely a collection of top-notch performances, however. The beautiful, frozen locations emphasize Nightmute’s isolation. Dormer’s near drowning during a chase with Finch is gorgeous and exciting, as well as dreadfully ironic – the only chance Dormer has at darkness, and he has to claw his way out into the sun. The mysterious momentary flashbacks and sleep-deprived hallucinations that plague Dormer complete the atmosphere of unease. Ultimately, “Insomnia” ends up surreal, engrossing and, despite its perennial daylight, quite dark.