You may not have heard of young Australian actress Abbie Cornish, but chances are you're going to know exactly who she is pretty soon. Cornish won Best Actress at the AFI (Australian Film Institute) Awards in 2004 for her role as Heidi, the runaway teen in Somersault, and she's followed up that role with a slew of roles in upcoming films, including Candy with Heath Ledger, Ridley Scott's A Good Year with Russell Crowe, and Elizabeth: The Golden Age, with Cate Blanchett. At least part of the reason you'll be seeing more of Cornish in the near future is her performance in Somersault.

Cornish plays Heidi, a 16-year-old who runs away after being caught by her mother making an awkward sexual advance on mom's boyfriend. Over the next two or so hours, we follow Heidi's progress (or lack thereof) in learning to navigate relationships with the opposite sex. That's pretty much all there is to the movie, and yet it's one of the most memorable films I've seen in a long while, thanks in large part to Cornish's remarkable performance capturing the essence of this lost, lonely woman-child struggling to make her way.

Along the way, Heidi meets Joe, an equally lost soul who is unable to connect emotionally with anyone. We get about as much information as to the why of this as Heidi does -- that is to say, not a lot -- and consequently we feel her pain and frustration as she tries to establish ties with her enigmatic and resistant lover, who is floundering in the sea of his own sexual identity.

Somersault is rather an enigmatic film; it's far more a character study than a narrative, and yet, on the surface, one might think there's not a lot of character development going on. But the soul of a person isn't always shaped by vast, obvious changes; growth often tends to happen more like the work of a sculptor working in marble, with a finely placed chisel shaving bits at a time until the beauty within the block of seemingly impermeable stone is revealed. Such is the case with the subtle molding of Heidi's character in this carefully crafted film.

The moment after Heidi's mother catches her making a move on her boyfriend is a moment that anyone who's ever been a teenager can likely relate to -- that moment of impulsively breaking free of the bonds of childhood to experiment in the realm of adulthood, followed by the intractable consequence of those actions. Heidi, instantly a child again when she realizes what she's wrought, holds out her arms to her mother for comfort, only to have her mother reject her. Cut to the quick by the fear that her actions have cost her mother-love forever, Heidi once again (unwisely, perhaps) follows her impulsiveness and runs away to cold, snowy, Jindabyne. The dismal location serves almost as a parable for Heidi's fear and loneliness, and it isn't long before she is once again attempting to fill the emptiness inside her through short-lived sexual escapades.

Heidi's journey from impulsive, friendless waif to a young woman gaining an understanding of real love and friendship is the heart of the story. Cornish perfectly conveys the lonely desperation of a young girl, with no stable father figure or model of a healthy romantic relationship to use as a model, trying to figure out how to make people love her. Heidi is a like a lot of young girls I know, telegraphing her desperation to please and be loved to every male her path crosses, and punishing herself in order to gain attention. In the process of sloughing through a world where double standards brand her a tramp, while the young men she engages with suffer no such retribution, she learns, one hopes, that she must first love and respect herself, regardless of what others may think of her.

Writer-director Cate Shortland shows a good understanding of adolescent girlhood, and uses a muted palette to set a fairly somber mood in keeping with the story. Good performances by Sam Worthington as Joe, Heidi's intermittent lover, who finds himself unwillingly drawn to her in spite of being walled off emotionally to the world, and Lynette Curran as Irene, the motherly motel owner who has lost her adult son to a tragedy of his own making, help bolster the film, but Cornish is its focus. In the hands of a lesser actress, this could have been a disaster, but Cornish keeps you intrigued enough about Heidi and what will become of her that you're willing to stay around, in spite of the lack of strong storyline. Watching a film like Somersault is a bit like being a fly on the wall of a stranger's life for a while; some lives are more interesting than others, and thanks to Cornish, Heidi's tale haunts long after the closing credits roll.