Arrested development: "Young Adult"

The heroine of Jason Reitman's new comedy Young Adult is defined almost entirely by her lifestyle choices. Three times in the opening fifteen minutes, her television is shown tuned to Keeping Up with the Kardashians. The credit sequence finds her repeatedly rewinding a cassette (signifier enough in itself) to hear the one part of the Teenage Fanclub track she wants to listen to, and we grasp that not only has this woman failed to move on from the 1990s, she can't even get past the chorus of this one song. She goes out in the same clothes she wakes up in; she regards a tub of Ben & Jerry's as a square meal. I spent the film's ninety minutes in a state of some considerable vacillation, uncertain whether the gal was a total nightmare, or my own personal dream woman.

This is Mavis Geary (Charlize Theron), a divorced thirtysomething writer with alcoholic and depressive tendencies, and her sole means of support is the young-adult fiction franchise she's taken over from its creator at the point when sales began to plummet. We find her facing up to the challenge of finishing up the franchise's latest instalment - it's not going well - and a secondary task, more pressing yet: trying to make her haphazard lifestyle fit with anybody else's. This L-word is crucial: it strikes me that Reitman (Juno, Up in the Air) is making the kind of lifestyle movies most contemporary romantic comedies aspire to be - Mavis could be an indie chick Bridget Jones - only elevated by the director's choices with scripts and actors. Here, he's reunited with Juno's Diablo Cody, whose screenplay is structured around a homecoming of sorts: Mavis is spurred to drive back from Minneapolis to her Minnesota birthplace (in American terms, the shortest possible distance from where she began) in an almost certainly doomed attempt to reunite with her happily married, new-parent high-school sweetheart (Patrick Wilson).

With its underlying theme of personal and social immobility, Young Adult feels like a sister movie to Up in the Air, though there are clear distinctions between the two. In the latter, Clooney's Ryan Bingham was unmistakably mature, and in search of something more permanent still. By contrast, Mavis, like the genre of fiction she's working within, is a half-and-half: she has the trappings of a responsible adult (the job, the apartment), but none of the sense of responsibility. Instead, she lives, like so many, in a state of frantic uncertainty, haring from moment to moment, throwing bad choice after bad choice, and - when all else fails - booking herself in for regular mani-pedis to give herself at least the comforting illusion of transformation. Winning back her ex appears just another of those crazy projects she's doomed to abandon halfway through.

Cody and Reitman, for their part, work assiduously towards a definition of a type we may know all too well. The spectre of Bridget Jones keeps coming back: Mavis, too, is presented with a choice between two men, so diametrically opposed as to seem like psychic projections. Wilson's ideal is a still-hunky househusband whose potency is never in doubt from the moment snaps of his new baby drop in Mavis's inbox. Reality, of a sort, is represented by Patton Oswalt as a squat moonshiner, apparently left literally dickless after a vicious high-school beating. The film builds a very peculiar tension from this either-or, because a) the uxorious Wilson, despite Mavis's concerted attempts to ply him with booze, clearly isn't interested in her advances, and b) we can be fairly certain that in no movie world is Patton Oswalt going to end up with Charlize Theron, even a messy Charlize Theron.

Cody, while ditching the teenspeak of her earlier scripts, continues to pen razor-sharp setpieces - like the baby shower that effectively becomes an intervention - and double-edged lines. (One peer tells Mavis "the rest of us changed; you got lucky".) If the whole isn't quite as emotionally resonant as the filmmakers' very best work, Young Adult remains a well-turned vignette, interestingly poised at the cusp of social comedy and the kind of psychothriller Cody attempted in Jennifer's Body, as this hellbent ex insinuates herself into the Wilson household with the express intention of shattering its happiness into a thousand tiny pieces. By way of a bonus, it's also an effective showcase for the still underused (or maybe just wisely picky) Theron, playing a character who - whatever you make of her, whether nightmare or dream woman - isn't entirely sympathetic. It's just possible Cody may have been extending a pointed fingernail in the direction of writers like Stephenie Meyer, who use their fiction to espouse very personal hang-ups, but Theron makes Mavis a person rather than punchbag: hungover and grouchy, clutching to her delusions, tearing out her hair from a sense of being almost terminally behind the curve, and having to scrabble twice as hard simply to find her feet in the morning.

Young Adult opens in cinemas nationwide tomorrow.