"Baron Munchausen," she said, "really defined me in terms of never really wanting to be on huge films ever, and really focusing on independent films. There's a real fear in me of never wanting to be in an unsafe environment again."

Doug Liman, a good friend of Polley's who directed her in "Go," is a victim of her wariness. "I've offered Sarah a part in everything I've made since 'Go,' including the female lead in 'The Bourne Identity,' and she keeps turning me down," he said. "She has a tremendous amount of ambivalence about this profession, but that makes her a better actress. She has no interest in seeing herself in a magazine, but she does have an acute sensitivity to real human beings. Even going out for lunch with her, it's hard to scream, 'Where's my Diet Coke?' when Sarah has just been incredibly kind to the waitress."

Post-Gilliam, Polley hit child stardom in Canada playing the precocious lead in the television series "Avonlea," a prairie period drama that eventually ran in the United States on the Disney Channel. Two days after she turned 11, her mother died of cancer. A few months later, Polley developed scoliosis, a severe curvature of the spine. Between the ages of 11 and 15, she wore a fiberglass brace for 16 hours a day, enduring painful welts and humiliating costume fittings to accommodate the bulky, corset-like contraption. Then, at 15, she underwent a 10-hour operation and spent a year in bed recovering (the rods still in her back occasionally set off alarms at airport-security checkpoints).

"The thing about Sarah is, she's only 28 but she's been through quite a lot in her life," said Olympia Dukakis, who plays the pragmatic wife of Fiona's mute boyfriend in "Away From Her." "She seems very sweet, and she is, but she's not frivolous. It's a metaphor: she's got a rod up her back. You can see it in her acting. It's a kind of steeliness."

Polley never finished high school, but she read widely, and to the left. In the early '90s, she joined a growing political movement in Toronto, handing out socialist newsletters and organizing protests against the neoconservative provincial government.

After several months, Polley's political obsessions were making her, as she put it, "boring, dogmatic, narrow." When Egoyan invited her to return to acting with the lead role of the incest-victim narrator in "The Sweet Hereafter," she agreed, but expected to quickly return to her political activities.

"It seemed like a nice little ending to my acting career to work with Atom, and then it ended up sort of being the beginning of it," she said.

The film was a critical smash, earning Egoyan a best-director Oscar nomination. In short order, Polley appeared in "Go" and "Guinevere," in which she played the young lover of an older Stephen Rea.