Ashley becomes jealous when, during a slumber party, Mary-Kate reveals that she has kissed a boy; After Paul finds out Carrie was over at Kevin's he assumes their relationship is more than it actually is - which leads to rumors about them being a couple.

Mary-Kate and Ashley switch costumes with Max and Brian so that they can attend Carrie's Halloween party, from which they were banned by Kevin.

Mary-Kate and Ashley prepare for their first school dance. Mary-Kate wants to dance with Jeremy, but he tells her that he only knows how to swing dance. Carrie teaches Mary-Kate how to swing dance. At the dance, however, they learn that Jeremy doesn't know how to swing dance at all - he lied to her because he doesn't know how to dance.

Carrie's old boyfriend, Alex Reardon, is back in town and Carrie feels she must make herself look as successful as he is. Carrie convinces Kevin to pretend to be Carrie's fiance to make Alex jealous; The twins have a party which doesn't go quite as planned.

Mary-Kate is forced to teach Ashley all about sports when she develops a crush on Eric, a sports fan; Kevin must appoligize to Carrie when he causes waves in their friendship.

Trouble starts when Carrie moves into Kevin's basement.

Kevin is not pleased when his brother, Matt, comes to visit. Kevin knows his brother is immature and unreliable, which becomes increasingly clear after an incident at a hockey game.

The twins are paired up with male partners for a school assignment to teach them about marriage; Against Kevin's wishes, Carrie goes on a date with Matt.

Kevin realizes that he is bored with his inhibited girlfriend, Nancy, and agonizes over how to end the relationship. When he tries, Nancy misinterprets him and becomes even more serious about him. Matt's advice is of no use, and Carrie is upset because Nancy is her friend. Finally, Kevin gently reveals his true feelings to Nancy, who overreacts. Carrie appreciates that Kevin is sensitive and unwilling to be cruel. Meanwhile, knowing how much Mary-Kate loved horseback riding when her mother was alive, Carrie invites her to come on Carrie's weekly ride. Mary-Kate declines, puzzling Kevin. But Carrie finds out that Mary-Kate secretly visits the stables every day. Mary-Kate admits to Kevin that she doesn't want to remind him of his wife, and he assures her it's okay because it is a good memory. Also, Ashley gets into trouble when she secretly orders a handbag over the Internet using Kevin's credit card.

Carrie has plans to go to South America for the summer. The twins trick Kevin and Carrie into having dinner together at a restaurant. At the airport, Kevin is disappointed to see Carrie is traveling to South America with a classmate. Carrie kisses Kevin, and boards the plane.

To be accepted to the cheerleading squad Ashley must perform a mean prank on Mary-Kate's new friend, Gabrielle. Ashley soon learns that nothing is worth doing something so mean to another person; Carrie convinces Kevin to take a day off work and the two go to a ballgame together.