It's been six months since Nicole (VINESSA SHAW) dumped Matt (JOSH HARTNETT), and he's yet to get over that or her. Despite having no problem finding other women to date or bed, he can't stop thinking about her and that's caused him to experience some sexual problems. His roommate, Ryan (PAULO COSTANZO), thinks he should just get on with his life, as does Matt's brother, John (ADAM TRESE), a priest in training.
When Matt hears from the "Bagel Guy" (MICHAEL C. MARONNA) that Nicole is now engaged, it just about breaks him. Yet, he decides to do something about that and his other problem, and that's give up sex or any other sort of sexual behavior for Lent. Most everyone thinks he's crazy and/or won't be able to accomplish the task, with his co-workers secretly setting up a website and betting pool related to such matters and when he'll fail.
Matt thinks he'll have no problem completing his task, but then meets Erica (SHANNYN SOSSAMON), a young and attractive woman who scours porn sites for a living working for a company that provides software to filter them out. Although Matt tries to keep things platonic, he and Erica begin developing feelings toward each other, although he decides not to tell her of his quest, a point that leaves her and her roommate, Sam (MAGGIE GYLLENHAAL), wondering what his story might be.
As the days wear on and Matt's older boss, Jerry (GRIFFIN DUNNE), decides to try his hand at abstinence as well, various people try to make Matt succumb to the temptations of having sex so that they can will the ever-growing betting pool. Yet, he tries to hold on and hopes that Erica can wait for his unique goal to be over.