One of the drawbacks of being a movie actor is that you might someday have to watch yourself run. Jim Carrey is facing such a moment right now, and he's not proud of what he sees. The actor and his costar Kate Winslet are crunched around a monitor in New York's Grand Central Terminal watching playback of Carrey dashing across the main concourse. "Man," says Carrey, "I run like such a geek. It's because I'm Canadian. I look like a goose." Fortunately, it's nearly midnight, so only a few dozen commuters witnessed his graceless gallop. But "Eternal Sunshine of the Spotless Mind," Carrey's new film, will eventually show in thousands of theaters. So his director, Frenchman Michel Gondry, who probably also runs funny, suggests another take. As Carrey rushes off, a traveler stops him for directions to a train. Later, he's asked what he said. Carrey puffs himself up, mock-theatrically: "Out of my way! I'm in the movies!"

He's never been in one quite like this. "Eternal Sunshine" tells the story of Joel (Carrey), a meek introvert who's just been dumped by his girlfriend, a silver-tongued pixie named Clementine (Winslet). Joel soon learns that Clementine has gone to outrageous lengths to move on: she's had an experimental surgery to erase all memory of him from her brain. Enraged, Joel signs up for the same procedure--but halfway through, he changes his mind and begins literally racing through his own memories to preserve even one last image of his ex-darling Clementine. It's a funny, bewildering and unexpectedly touching tale about how the experience of a relationship can matter so much more than its outcome.

Along with Carrey and Winslet, "Eternal Sunshine" also features Kirsten Dunst and hobbit hero Elijah Wood; together they've starred in seven of the 30 highest-grossing movies ever made. But each took a pay cut for this $27 million oddity--all because of two men: Gondry, a trailblazing music-video director, and Charlie Kaufman, the Oscar-nominated author of "Being John Malkovich" and "Adaptation." "Those two were thick as thieves" on the set, says Winslet. "I remember wishing I could be a fly on the wall. I mean, how on earth did they come up with this insane story?"

In fact, the inspiration for "Eternal Sunshine" came from an artist pal of Gondry's, who wondered how friends would react if they received a card saying they'd been deleted from his memory. Gondry loved the idea and asked Kaufman, with whom he'd partnered on the unheralded 2001 comedy "Human Nature," to build a script around it. As usual, Kaufman resisted going the Hollywood route with the conceit--"writing a 'he's got a secret and he doesn't know what the secret is and someone's trying to kill him for it' kind of thing." (Hollywood, evidently, could not resist. Hence "Paycheck.") "We wanted to do something real," says Kaufman. "The sci-fi aspect was just a device to tell a relationship story." The movie's title comes from a poem by the 18th-century English neoclassicist Alexander Pope about a woman mourning a lost love. Kaufman is known for writing autobiographically, and he may see Pope, who was 4 feet 6, as an exaggerated version of himself: small, shy and cerebral.

"Eternal Sunshine's" Joel is also quite Kaufmanesque, so who better to play him than... gonzo comic superstar Jim Carrey? "When I first met Jim, I was very nervous," says Kaufman. "He's a big personality and I'm, you know, not. But he was very nice. He was very quiet. It was winter, and when he took off his hat his hair was a bit mussed up. He looked exactly like we wanted him to look in the movie." Carrey, meanwhile, is bracing himself for a hail of questions about why he's flipping back to drama after a comic smash like "Bruce Almighty." "See, that's the thing people don't get: it's all acting," he says. "Maybe it's just that I calm down a little in a part like this and let you see what's already there. But it's always there, even in 'Ace Ventura'."

The movie's 14-week shoot, which spanned New York's bitterest winter in ages, was a ragtag guerrilla operation, with the irrepressibly spontaneous Gondry concocting new scenes on the fly. Carrey and Winslet loved it. As the movie unfolds, Joel's memories get blurrier and more surreal; in one lovely moment, he wakes up next to Clementine on a snow-covered beach. The script called for a clear, sunny day, but a storm wrecked the plan. So Gondry adjusted. "Suddenly," Winslet recalls, "he yelled, 'I know whats we do! We just put ze bed on ze f---ing beach!" Ze scene, like ze movie, is one of a kind.