Life in the fishing business is tough these days. Sean's Dad has been losing money every trip; poring over the accounts, Sean knows that they're reaching crisis point; soon they'll have to sell the boat, his Dad's pride and joy, the vessel on which he has worked all his life and which he had hoped to pass on. There seems to be no way out. Perhaps, Sean thinks, he can keep things going for a little while longer if he smuggles some cigarettes across to Scotland from Europe, bypassing customs. But the man with whom he hopes to make this deal has other ideas. When Sean is offered thousands of pounds to smuggle Chinese illegal immigrants hoping to start a new life, it seems too good to be true. There's a reason for that.

True North is an unremittingly grim and claustrophobic portrayal of life in desperate circumstances, but it's engagingly told, threaded through with humour, and it makes for compulsive viewing. Martin Compston, as Sean, shows that his youthful promise was no fluke, even if he's making quite a habit of appearing in what are essentially Greek tragedies. Peter Mullan, as the crewman who helps him, is at his very best, providing a strong moral centre to the film. Early images of him enjoying his shore leave in a little blond wig are quite as disturbing as anything you'll see later on, but set the tone nicely, confirming him as a happy-go-lucky guy whose strong spirit has kept the others going in hard times - but as things get really hard, he too will find himself out of his depth and questioning his own motives.

Steven Robertson turns in a delicately judged performance as the ship's cook, a young man who seems to be harboring urges and anxieties which the others have scarcely guessed at, trying to do the right thing despite himself. The ambiguity of each of these characters is the film's greatest strength, enabling the development of astute sub-plots which ably support the main story. The only weak link is Gary Lewis as the skipper. In a role which requires him to be quiet and brooding, he just doesn't quite have the presence to match up to the rest of the cast. We find ourselves concerned about his fate for Sean's sake rather than for his own. Nevertheless, the interaction of these four men - occasionally witnessed by the small girl who has stowed away rather than be shut in the hold with her compatriots - is always gripping.

In a remarkable demonstration of technical prowess, True North was filmed aboard a real trawler. Watching it force its way through rough weather lends a real edge to proceedings, a constant sense of danger. This is intense film-making, and it's also politically intense, continually drawing parallels between the economic pressures on the fishermen, the migrants, and sex industry workers, questioning how much freedom any of them really have - yet it never allows this to let individuals off the hook when it comes to moral choices. Though solidly grounded in contemporary issues, it is, at the same time, a classic fable of the sort which never loses relevance.