Jane Goodale (ASHLEY JUDD) is a talent booker for the Diane Roberts Show, a New York talk show that's just been picked up nationally. Beyond finding talent for the show's ambitious host (ELLEN BARKIN), Jane spends her time trying to figure out why men always dump her. In doing so, she's come up with her "New Cow Theory" where she equates men with bulls who show no interest in cows with which they've already mated, but instead pursue new cows.
One of her coworkers, Eddie Alden (HUGH JACKMAN), seems to be the epitome of her theory as he appears to her as a carefree womanizer, who always moves on from one woman to the next after bedding them. Despite her theory, Jane is immediately smitten with and then falls for Ray Brown (GREG KINNEAR), the show's executive producer who's just arrived in town.
Although he has a girlfriend of three years, Ray and Jane soon become lovers and she couldn't be happier, a point that doesn't sit well with her cynical editor friend, Liz (MARISA TOMEI). Yet, just when things seem to be going so right and she's given up her apartment to move in with Ray, he dumps her, forcing Jane to rent a vacant room from Eddie.
As the two of them clash and bicker about how men and women view relationships, and she watches how her sister, Alice (CATHERINE DENT) and her husband, Stephen (PETER FRIEDMAN), get along, Jane eventually puts her theory into print, creating a national sensation. While doing so and trying to deal with her feelings toward Ray, she doesn't realize that the best thing for her could be right under her nose.