Ugly truth beautifully told

David Mackenzie's film is about a crisis of conscience in a man who doesn't have one. Based on Scottish Beat writer Alexander Trocchi's 1957 novel, it is a rare thing: an elegantly-constructed movie of inimitable ugliness, a beautiful film about repellent people, a journey that leaves its protagonist by the end in exactly the same state of moral atrophy in which he began.

Joe (Ewan McGregor) is treading water. A feckless drifter, he is working on a coal barge with Les (Peter Mullan), his wife, Ella (Tilda Swinton) and their young son, Jim (Jack McElhone). The period is the Fifties, the place is the Clyde canal stretch between Glasgow and Edinburgh.

When Joe and Les fish a young girl's corpse from the water, it leads to a chain of events that upsets the fragile ecology of the claustrophobic relationships on board: Joe seduces Ella; Ella gradually takes control; Les leaves and Joe takes his place. Meanwhile, the girl's death is under investigation. In a series of flashbacks, it becomes clear that the girl, Cathie (Emily Mortimer), and Joe were lovers, who broke up but had a brief regrouping just before tragedy struck her. Joe allows another man to be implicated in her death - his conscience is pricked, but fails to bleed.

That Joe is a failure is clear from the outset. But quite what he has failed at does not become clear until later. Of course, there are clues; his description of the "imagined" circumstances of Cathie's death is clearly that of a writer. As a cipher for Trocchi himself, a writer who struggled with the demons of heroin addiction and alienation, Joe is a kind of shadow puppet. Joe's addictions are hand-rolled cigarettes and sex.

Mackenzie is a gifted director. In this, his second feature film, he creates a sense of time and place with extraordinary economy and very little expository dialogue. The dark interiors - the barge lit by oil lamps, the gaslit pubs - suggest an almost 18thcentury atmosphere. And he conveys with calibrated precision the uncomfortable intimacy of the situation, from Cathie's barely-clothed corpse to the two men scrubbing each other's backs on the docks at the end of the working day.

This is McGregor's most mature and subtle performance to date: even in sunlight, his Joe seems to walk in shadow as if he had forfeited the right to natural warmth. With minimum dialogue, he conveys Joe's internal blankness and frustration beautifully, despite the fact that his character remains an enigma.

In a performance of naked courage, Emily Mortimer shows that she is prepared to go to extreme lengths of masochism in her depiction of a woman undone by love, while Peter Mullan is reliably solid as Les. But the real revelation is Tilda Swinton, whose Ella is the one character to demonstrate any real development. A woman who has lived her whole life on barges, going about her duties with grim efficiency, she discovers her sexual identity and a different kind of feminine power. Then, when she lets slip her dream of a domestic future with Joe and Jim in a little bungalow (a prospect that horrifies Joe), the fragility beneath her rawboned strength is revealed.

The sex scenes are gritty, literally. Pale, unclad bodies look especially vulnerable against the hard abrasive surfaces of walls, and dockside grounds. And the cataclysmic scene when Cathie and Joe get to slippery grips on the floor covered in custard is sudden, shocking and explosive.

Joe may be an outsider in the existential manner but he is Camus Lite, not freighted with tragic momentum. His one redemptive act - saving Jim from a watery death in the canal - is performed without thought, a subconscious reaction to the earlier drowning. He is a man standing still in his own soul, as one sequence illustrates with a quiet brilliance. From a fixed overhead position, we see the barge passing beneath the camera while Joe walks its length, maintaining the same position on screen. Everything is moving in the shot - the water, the barge and Joe himself - but the impression is that he is standing still, going nowhere, walking up the down escalator of his life.

This one moment conveys everything you need to know about his character. And the mirror given to him by Cathie with the inscription "Think of me when you look at yourself" provides the symbolic coda. When Joe finally tosses it away it is not because he cannot bear to think of her but that he can no longer face himself. A grim, intelligent and fiercely compelling film.

Young Adam
Cert: 18