HE HAS ENTRANCED her with his confidence, and heady jazz music, and Alfred Stieglitz's nude studies of Georgia O'Keeffe -- and now he's calmly cooing at her, moving in for the kill. But he hardly moves at all. She sits across the way in his living room, not looking at him but wanting him, wracked with uncontrollable, nervous laughter. Then he pounces, but it's her body that makes the first move. This cat-and-mouse seduction, with its hair's-breadth power shifts, is the key scene in Guinevere, Audrey Wells' insightful new film. Its players, Stephen Rea and Sarah Polley, give performances of remarkable unaffectedness.

In preparation for writing about this film, I had trouble coming up with another American film like it. My first inclination was to reach all the way back to Natalie Wood, for chrissake, being disillusioned by Gene Kelly in the 1958 Marjorie Morningstar, and then jump 20 years ahead to Girlfriends, Claudia Weill's amiable 1978 film about self-discovery -- though both films, to different degrees, put sexuality on the side burner. Victor Nunez's patchy, ambling Ruby in Paradise, with Ashley Judd's auspicious debut, came to mind. Nothing that I can recall, though, has Guinevere's particular kind of awakening: a biting, clear-eyed but not heartless take on the ambiguities of becoming a young woman in the presence of a man.

It seems every time a middle-aged male writer gets misty, we get treated to another golden-hued look at the first sexual conquest of some callow youth, often at the hands of an incredibly voracious woman (think Summer of '42, then move all the way down to Porky's). Wells (who previously wrote the sappy The Truth About Cats and Dogs, and is making her directorial debut with Guinevere) is going for something different.

In telling the story of Harper (Polley), a crushingly insecure 20-year-old who embarks on an affair with a photographer (Rea) who is at least twice her age, Wells is able to not only deal honestly with female sexuality, but to present it and its accompanying personal growth in a light that does not completely defame the involvement of a Lothario.

The film is no masterpiece, and I have a feeling it won't work for everybody. Wells stacks the deck a bit too heavily against Harper. Her family is a TV drama study in WASP dysfunction, complete with a bitter and slightly boozy matriarch (well-played by Jean Smart). There's a cool polish to the film where others might want some edges. With its ethereal pop score and occasionally flamboyant romantic gestures, it sometimes goes over like a slightly sinister Jerry Maguire, which I'm not sure is altogether the wrong tone (this is, after all, the reverie of a young, upper- middle-class woman). The recollection is far from untainted, but perhaps most frustratingly for some, it's made clear that Harper has come out with some rewards from the experience.

Polley is perfectly cast and completely human as Harper. It's the type of role she's played before; Peter Wellington's excellent, under-seen Canadian film Joe's So Mean to Josephine detailed her character's self discovery during an affair with brutish, gorgeous Eric Thal. Wells expands upon that vulnerability and guides her through what may be a quintessential role. Self-effacing yet singular, Polley rides a fine line between forcing the performance and not doing enough. The languid, indelicate way she fumbles with her pearl necklace in the opening scene is only a hint of the extraordinary awkwardness she'll reveal later. Guinevere is a film filled with momentous but fleeting glances and touches -- a hand on the shoulder, a finger on the neck -- and Polley is all rolling eyes and desperate limbs. She often looks like she has either nothing to say or a huge secret she'd just rather not tell you.

Rea complements her in a brave, complex take on The Older Man. Even in some of the film's few lapses into overstatement (with Rea wearing a ridiculous hipster scarf, for instance), he's so unabashedly direct that he emits an air of honesty even when we know he's lying. Rea manages the difficult task of creating a casually cruel man who may not even recognize his own lies anymore, and would prefer not to regain that ability. Finally shamed in front of Polley, Rea takes a sad, searing close-up through a car window that explains more about him than any dialogue.

"He was the worst man I'd ever met, or maybe the best," Harper reflects in the opening voice-over, "I'm still not sure." For whatever else she may do too slickly, you have to give Audrey Wells this: She made a film in the United States which shows a rite of passage -- a woman's rite of passage -- as an event with no losers and no winners. Only participants.