Early in Nowhere Boy, Mimi Smith (Kristin Scott Thomas) stands by the open grave at her husband's (David Threlfall) funeral. She is a strict woman, well into middle age, fiercely proud of her lower-middle-class English propriety, and what we have seen of her to this point makes us wonder if she has genuine human feelings. And yet, as she stares at her husband's coffin, her face is drained, and her eyes bespeak inward misery and pain which she will never, ever permit anyone else to see. Captured by the suburban life she fights with tooth and claw to protect, she maintains at all time a chilly composure, but the cost of doing so is dear. All this is expressed in just a flash, but it is as perfect a moment of acting as I think I've seen this year, not that any of us need to have it pointed out that Scott Thomas is a breathtaking brilliant actress. But it's fun to point it out anyway. Because she totally is, and she is as heartbreaking and true in Nowhere Boy as the most ardent of her fans could ever hope for.

Damn shame that it's not her movie. That, really, the movie doesn't much care about Mimi Smith at all, except that she had a nephew, the nowhere boy of the title. Smith's nephew, played by Aaron Johnson, was a cocky troublemaker in 1950s Liverpool by the name of John Lennon, and I suspect you've maybe heard about him. Nowhere Boy certainly expects that you have. Not since The Motorcycle Diaries failed to have anything even borderline-interesting to say about Che Guevara six years ago has a biopic staked so very much on the notion that, since somebody grew up to be famous, it must be fascinating to take a look at his pre-stardom youth.

In truth, Lennon's childhood was fairly dramatic: at the age of five, he was taken by his aunt from his ditzy mother Julia (Anne-Marie Duff), right around the time that his father Alf was about to leave for New Zealand and hoped to bring the boy along. From then on, Lennon lived with Mimi and her husband George as his de facto parents, having an extremely strained relationship with his birth mother than only began to thaw out when the boy drew near to his late teens (the film rather significantly re-characterises their relationship as even more estranged than it was in actuality; the onscreen implication is that he hasn't seen her for years as of 1955, which simply isn't true). Having finally found the outspoken affection he never received from the loving but undemonstrative Mimi, Lennon was shattered when she died in a car accident in July, 1958, when he was all of 17. This event haunted him for years to come: his soul-searching 1970 album Plastic Ono Band opens with a track titled "Mother" ("I wanted you, but you didn't want me"), and closes with "My Mummy's Dead" ("I can't get it through my head / Though it's been so many years").

This narrative, invisibly rejiggered to make the passage of time seem shorter (George Smith died three years before Julia Lennon; the film makes it seem rather closer to one year), is dutifully recapitulated, along with John's quest to start a rock & roll group (but only after he'd already taken to copying rock imagery, in the eternal manner of the hipster) with best friend Pete Shotton (Josh Bolt), a few spear-carrying guys, and an alarmingly cherubic younger boy named Paul McCartney (Thomas Brodie Sangster). This is emphatically not the story of how The Beatles were formed. The name of the band is never spoken, in the most conspicuous possible way. This is probably for the best (consider the tepid & forgotten 1994 feature Backbeat, which picks up at nearly the instant Nowhere Boy ends), but in so scrupulously avoiding any hint of where Lennon's career as a musician would end up, the filmmakers hamstring themselves: by refusing to consider where Lennon's personal misfortunes would end up driving him, they are left with only the sensational details of his adolescence, and the film ends up being a good deal too melodramatic to function terribly well as a self-contained character study, which is the only thing that it could be, cutting off where it does.

(It's doubly frustrating that Nowhere Boy does so little as a biopic or as a tale of personal anguish, given that screenwriter Matt Greenhalgh's last project, Control, managed to be such a fantastic swim through the hurt mind of Ian Curtis, despite never directly mentioning the prominence or importance of Joy Division).

The film is the feature directorial debut of Sam Taylor-Wood, an important conceptual artist and photographer; one would assume that a primarily visual artist would bring something aesthetically bold and probing to the life story of a man who became well known for his avant-garde proclivities later in life, but it is not so. Other than a short montage depicting Lennon's attempts to learn guitar, played against a fast-motion background of life moving around him, there's nothing even imaginative about the visuals; they are tastefully drab, and the use of color is vaguely intriguing - particularly in the costuming - but otherwise the film is intensely straightforward, the clear sign of a newbie filmmaker who wants to be certain that she "gets" cinema before she starts to play around with the medium. Then again, the film was shot by Seamus McGarvey, a cinematographer whose career is largely made up of tasteful, straightforward work (save for, arguably, his two collaborations with Joe Wright), so maybe he's responsible.

As far as the acting goes, Scott Thomas is incredible, of course: capturing the motherly essence of her character without banging us over the head with it. Duff is also fairly great, playing Julia Lennon as a blowsy farce of a character, a woman in her 40s who refuses to stop acting like a teenager. It's a role that could readily tip into parody, and almost does in the handful of moments when Greenhalgh and Taylor-Wood regrettably amp up the Oedipal overtones; but Duff is always able to bring the character back to ground, finding the human quality which drives the film's Julia (whom I'm not convinced is exactly identical with Julia-in-reality) to her extravagance as a means to hide her own pain. The two actresses both, in essence, play the same crisis - a mother dealing with her feelings of possessiveness and abandonment - but in finding such different ways to express that crisis, give Nowhere Boy the most credible spark of psychological insight it has.

A pity, then, that Johnson's take on Lennon is so superficial: a generic angry kid flailing about against whatever comes his way. Wisely not attempting to perform a Lennon impersonation, Johnson doesn't end up doing much of anything in its place, though the script, to be fair, doesn't exactly provide such a robust vision of its subject that anyone but a truly great actor could pull something out of it. Like most art about Lennon, Nowhere Boy plays in no small way as a Life of St. John text, so awed by its subject that it refuses to actually grapple with him, and that leaves Johnson with nowhere to go.

At the end, Taylor-Wood indulges in a somewhat infuriating photo montage that serves only to further emphasise that the film's ultimate purpose is hagiography, but there is one snapshot that deserves special consideration: it's Mimi and Lennon, smiling broadly, and it's credited to 1965. 1965, the year of Help! the film and album, Rubber Soul, the first drug experiments, Shea Stadium. A year in which Lennon's cultured cynicism of 1957 had hardened through Beatlemania and a crazed degree of international prominence that no 25-year-old should ever have to deal with. And yet there he is, with his beloved aunt-mother, genuinely smiling and looking years younger than he does in most other pictures from that period. It's a powerful memento of just how deeply the connection between the two ran, and it's what all of Nowhere Boy would like to be about: the frustrated youth learning to express love. Unfortunately, despite the powerhouse work of two actresses giving everything they can to give that theme life, the movie has nowhere near the insight of that photograph. It's a generic story of a generic punk kid, who probably never became very interesting.