Scottish director David Mackenzie never makes films that go entirely orthodox ways. He's a director of some originality and power, and this adaptation of a novel by Peter Jinks gives him ample opportunity to confound expectations. It also gives Jamie Bell his best role since Billy Elliot.

Bell plays Hallam, half-boy, half-man, who spends his time spying on lovers from his Edinburgh treetop fortress and refusing to go to college. He is haunted by the apparent suicide of his mother, and obsessed with the idea that his father's new woman (Claire Forlani) has somehow killed her.

When she tries to befriend him by climbing up into his treetop, the enmity only strengthens - even though the two end up having a distinctly hostile kind of sex. So Hallam leaves home, comes across someone (Sophia Myles) he at first thinks is his mother, then begins to regard her as a potential lover when she gets him a job as a dishwasher at the hotel where she is manageress.

True to form, he climbs on the roof, spies on her in her room and watches as her married lover (Jamie Sives) gives her a rough seeing-to.

As you may now guess, this is a strange, if not rather weird movie about the perils of adolescence, a bit like (in the director's words) "a fucked-up version of Catcher in the Rye". You are perfectly at liberty to think that it might have been better as a book rather than a somewhat incredible film.

But, even so, Mackenzie's work is good enough to allow us to ignore our doubts. He makes Edinburgh seem a very real and rather beautiful city without once relapsing into touristy views. He gets his cast to act with conviction, even in the smallest parts. And he has in Bell a leading actor who never overplays, but gives us a portrait of a slightly cracked young man that is totally convincing.

This is no ordinary British film. It is beautiful to look at, thanks to Giles Nuttgen's cinematography, and has an imaginative and erotic edge to it that lifts it above the norm - even if sex is not the main purpose of Hallam's voyeurism.

Somehow the whole works surprisingly well, whether or not you end up thinking that it might have been still better left on the page.