A palpable sense of menace infuses this slow-burning Norwegian thriller, which is based on shocking, unsettling real-life events. Anchored by a terrific central performance from Aksel Hennie (Headhunters), the film sometimes strains to force the true story into a standard conspiracy movie structure. But it still has a bracing sense of urgency.

Hennie stars as Petter, Norway's top deep-sea diver, who in the early 1980s is recruited by the state-owned oil company to work with the Americans to lay a pipeline on the ocean floor connecting the mainland with off-shore drilling platforms. But this is uncharted territory for divers who will be working up to 400 metres below the surface. And when a test dive takes a fatal turn, Petter isn't convinced it was an accident. He certainly doesn't trust American diver Mike (Wes Bentley), but then everyone else is just as shifty.

Intriguingly, filmmaker Skjoldbjaerg shoots this in a gritty 1980s style tinged with the increasingly frazzled Petter's tenuous grip on reality. Diving this deep does something to the brain, so perhaps this is all in his mind. But Hennie is so likeable that we struggle with him to work out the truth, which means travelling through a Hitchcockian thriller in which everyone seems to be trying to kill him. This is fiercely clever filmmaking that's only let down because it's too clever for its own good.

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