Jenny (Uma Thurman), who later turns out to be the superhero G-Girl, begins dating Matt (Luke Wilson). When Jenny learns that Matt has affection for Hannah (Anna Faris, a coworker), she becomes furious and resorts to using her supernatural abilities to avenge him by wrecking his car, making him lose his job, etc.
Professor Bedlam (Eddie Izzard), the sworn enemy of G-Girl and hidden admirer of Jenny, contacts Matt. He enlists Matt in a plot that entails transferring G-abilities Girl into a meteor similar to the one that originally endowed her with them.
Cooperating, Matt invites Jenny to his flat, but when Hannah and Bedlam arrive, a fight breaks out. Each time Hannah and Jenny contact the meteor, they get comparable powers.
Jenny and Hannah use their abilities to fight, but Matt is able to persuade Jenny that she should be with Bedlam rather than Jenny because they weren’t meant to be together. Matt and Hannah ultimately make love, and Jenny and Bedlam share a kiss. The four of them get along well, and Hannah joins forces with G-Girl to rescue the day.