A grey trawler bobs through an inky black sea, dark clouds obscuring any stars in the sky. Only the moon breaks through to shed pale light on the murky blackness below. Welcome to the world of The Deep, a tense, harrowing drama from Baltasar Kormakur (a filmmaker from Iceland who also made Contraband (2012), an American production) that paints such a bleak but unforgettable picture of the North Atlantic Sea. Kormakur’s world, although ostensibly the Westman Islands off the south of Iceland, is like alien planet to the viewer, so vast are the seascapes and so barren the land.

This trawler, ploughing its way through the monochrome night, soon snags its net on a rock, and in a matter of minutes the boat has capsized and is sinking fast. The crew’s prospects are bleak and after some time only one is left alive, the overweight but spirited Gulli. It’s not a spoiler to say that he survives – the film is based on a true story and this is the key plot point around which the narrative hinges. Yet this isn’t just a survival-against-all-odds story, although it does do that to good effect. Instead, the final act of the film deals with the aftermath of the survival, the how and, intriguingly, the why of his miraculous return to land.

Kormakur directs with a steady hand, making the scenes at sea feel intimidating and gripping. The camera dips up and down beneath the waves to nauseating effect, and its closeness to Gulli as he spits, vomits and paddles his way through the ice cold water adds tension and discomfiting immediacy.

The pace drops off slightly once Gulli has made it to safety, and here the direction takes a back seat, giving lead actor Olafur Darru Olafsson a chance to showcase his formidable acting talent where previously he just spluttered and swam. As he is carted around different scientific observations, the film gently teases out questions of how one man can endure so much, and whether there can even be a rational explanation. The film’s opening made your heart pound but the thoughtful conclusion, centred by the mesmerising Olafsson, engages the brain in a pleasantly unexpected way.

The Deep is a visually striking and often harrowing tale of survival, lent extra thematic resonance by powerful performances and direction, as well as a final act that turns this true story into something even more unbelievable. The tagline promises miracles, and by the end of The Deep, you may just believe in them.