Joe, the conflicted hero/villain of David Mackenzie's sexy, secretive morality play ‘‘Young Adam,’’ is the sort of character one could easily envision Warren Beatty playing during his ’70s salad days: handsome, brooding, rakish, selfishly independent in a way that makes him irresistible and loathsome at the same time.

Alas, Beatty has grown out of such roles, leaving Ewan McGregor to pick this one up, with excellent results. Handed the biggest challenge of his career, the star of ‘‘Big Fish’’ and the various ‘‘Star Wars’’ prequels unearths a bitter, enigmatic performance that keeps us riveted to the last frame. It's the sort of performance that is full of suggestions — remorse, compassion, villainy — but like a superior wine, produces none of them outright.

Based on the novel by Scottish beat legend Alexander Trocchi, ‘‘Young Adam’’ begins in Lynchian fashion, when Joe — a rootless young drifter in 1950s Scotland — fishes a young woman's scantily clad corpse out of a canal near Glasgow. Stunned but strangely titillated by the discovery, Joe swiftly seduces Ella (Tilda Swinton from ‘‘The Deep End’’), the sour, angry wife of the barge owner (Joe Mullan) for whom he works. One shot of full-frontal McGregor nudity garnered the film an NC-17 rating, though anyone who goes strictly for the erotica is bound to be disappointed.

With tantalizing expertise, Mackenzie reveals Joe's other, more relevant secrets. We discover that he knows more about the dead woman (Emily Mortimer from ‘‘Love's Labour's Lost’’) than he initially let on.

We also get an explanation for his manner of speech, which seems awfully writerly for a mere deckhand. Gradually, a history emerges, one of sexual recklessness, artistic frustration and ebbing humanity.

Mackenzie, a BBC veteran making his feature debut, poetically underscores Joe's interior doubt with picturesque images of the barge drifting into fog, disappearing into darkened tunnels, etc.

Reflecting the zeitgeist of alienation and self-discovery that defined the beat movement, Joe is a stranger to himself, best illustrated in the scene where somebody asks him if he knew either of the bargemen who discovered the corpse. ‘‘I knew one of them,’’ Joe replies, presumably referring to someone other than himself.

Like the great character-driven movies of Bob Rafelson and Hal Ashby, ‘‘Young Adam’’ starts and ends ambiguously and trusts the viewers to hammer out their own judgments.

In the end, only one judgment is truly authoritative: Both McGregor and the movie are worth a look.