In just 30 finger-lickin' minutes of screen time in White Oleander, Robin Wright Penn swan dives into a snifter of Jack Daniel's, devours a carton of Camels, and fires off a six-shooter. Tarted up like Tammy Faye on prom night, she hijacks the picture as a God-fearing, gun-toting trailer-park queen aptly named Starr.

For the usually demure Penn, who's birthed a Gump and holds a place in the Gen-X hall of fame as the Princess Bride, squeezing into Starr's tube tops was an adventure. Still, when director Peter Kosminsky called, she tried to talk herself out of the job. "I don't think you want me," she told him. "I weigh like 100 pounds. I'm flat-chested."

"True," Kosminsky says, laughing. "In the book, Starr is described as having a huge bust. But she wasn't just a whore, and I didn't want her to be a cliché. I wanted a real, low-key, understated performance, and I knew Robin would do that brilliantly."

Flashing back to her junior-high days of turquoise eyeliner and banana clips "was an absolute blast," Penn says. She used the opportunity to delve into the ruptured psyche of a character who can quote the "Good Book" while speeding home in her station wagon to bed a married man. "I think it's the dichotomy of a woman's desperation—the need to be good, to repent," Penn explains. "But it's never coming from the heart. The only thing coming from her heart is that sense of desperation."