There’s plenty of nudity and explicit sex in David Mackenzie’s NC-17 adaptation of Scottish Beat writer Alexander Trocchi’s novel, but despite the fact that the sensual action involves Ewan McGregor, Tilda Swinton and Emily Mortimer, it’s hardly likely to titillate many viewers, and it’s certainly not the point of the film. Though “Young Adam” is called a thriller by the distributor, it’s less that than a character study of a scoundrel whose emotional detachment and callous use of the people (especially women) around him eventual lead him to an ethical dilemma that, typically, he ultimately avoids addressing.

The brooding picture is set in the grimy area surrounding the canals joining Glasgow and Edinburgh sometime during the 1950s, though the production design is intended to give it a timeless quality. As the film opens Joe Taylor (McGregor), a young drifter working (and bunking) on a barge, notices the body of a young woman floating in the water and fishes it onto the deck. He and his phlegmatic boss Les Gault (Peter Mullan), who also lives on the boat with his scruffy, hard-bitten wife Ella (Swinton) and their young son Jim (Jack McElhone), report the discovery to the police, and Les afterwards plays up his role in the matter and tries to keep up with the reports on the investigation. Meanwhile Joe, who spends most of his time reading, comes on to Ella, and she responds, particularly after he rescues Jim when the boy falls into the canal.

But eventually it’s made clear that Joe knows much more about the dead woman than he’s admitted. In fragmentary flashbacks it’s revealed that she was Cathie Dimly (Mortimer), whom he had an affair with and gotten pregnant during the time he was an aspiring writer. When another man is arrested for her murder, Joe–who by this time has replaced Les on the barge with Ella, its actual owner–must come to terms with his own guilt and the thought that innocent people may suffer for his misdeeds.

This synopsis gives the narrative thread rather more prominence than the film does. Essentially “Young Adam” is a dark, depressing portrait of an amoral young man and the people unfortunate enough to cross his path. His sexual conquests–not only of Ella and Cathie, but also of Ella’s sister Gwen (Therese Bradley), a crude, lascivious type with whom he shares a quick streetcorner connection–all have a grim, mechanical quality: there appears to be no real affection involved, merely selfish lust. Joe also treats Les with almost careless contempt, bedding his wife nearly within her husband’s sight line, and at one point he even admits that despite his rescue of Jim, he despises the kid and would prefer to have thrown him overboard than saved him. That’s why his concern over Cathie’s death, and even more over the arrest of her later boyfriend (a married man with children, no less) is so unusual. It makes it seem as though he might actually be developing a moral compass. But the power of self-preservation proves quite strong.

“Young Adam” is certainly impressive for its willingness to portray the harshness and casual brutality of these characters’ lives so unflinchingly, and Mackenzie deserves credit for the skill with which he captures the bleak, morally ambiguous atmosphere that envelops them. One must also admire the actors’ courage in playing unsympathetic types engaged in such cruel and humiliating conduct. McGregor is the most effective of them, especially in the early going; he conveys Joe’s easygoing charm, underlying nastiness and manipulative ability quite persuasively. His performance isn’t so successful in the later reels, when he becomes a more haunted, Dostoevskian figure, but it’s less his fault than the script’s. Swinton and Mullan both manage to submerge their natural star quality to become convincing as struggling, laconic, bedraggled denizens of the lower class, and Mortimer strikes all the right poses as a woman rather desperate for affection. (She also deserves recognition for enduring a scene in which Joe abuses Cathie with such foodstuffs as custard and catsup.) The film is certainly well-made, with moody widescreen cinematography by Giles Nuttgens, and there’s an insistent chamber score by David Byrne that adds to the somber, forbidding mood.

Still, when all is said and done, the film doesn’t prove terribly revealing or enlightening. That seems mostly the nature of the source material: the story successfully conveys the swirling, muddy waters of ethical emptiness, but it never goes beyond observation to any kind of deeper analysis or commentary. So as kitchen-sink dramas go, “Young Adam” is certainly effective enough, but as a portrait of a reckless, amoral man and his equally vacuous victims it doesn’t delve much beneath the surface; and though that surface has been drawn with considerable effect, in the end it’s not enough.