Trouble starts when Carrie moves into Kevin's basement.

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.

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.

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.

Ashley gets assigned Pokey Valentine, her crush, as a partner on a history project. She becomes jealous when Pokey and Mary-Kate begin spending time together.

Mary-Kate, who has had a bad past with animals, gets a homing pigeon which eventually flies away, causing heartbreak to Mary-Kate.

Ashley is excited when a model search for a teen magazine takes place at their school, but Mary-Kate is chosen over Ashley.

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 and Ashley places a bet with the school's fund raiser money; Carrie becomes jealous when Kevin starts dating one of her friends.

Kevin hires a tutor for Mary-Kate. Ashley convinces Mary-Kate to switch places so she can flirt with Taylor, the tutor, but their scheme doesn't go as planned; Carrie convinces Kevin to ask out a woman at a coffee shop.

When Kevin starts dating a woman, Marci, they fear that she will replace Carrie. The twins scheme to destroy Kevin and Marci's relationship.

Ashley makes a new friend, Nicole, which leads Mary-Kate to feel jealousy; Eddie and Kevin argue while Carrie tries to be a mediator.

After Kevin buys a new telescope, Mary-Kate and Ashley snoop into other people's business. They think they witness their neighbor, kindly old Mrs. Baker, murdering her elderly boyfriend, Mr. Fillmore. The situation gets even scarier for the twins when Kevin asks Mrs. Baker to take care of them so he can attend a jazz concert with Carrie. Meanwhile, Carrie hears Kevin play the saxophone and encourages him to perform for audiences as he used to.

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.

Mary-Kate and Ashley work as matchmakers to get Mrs. Baker and Mr. Fillmore together so that Carrie, a student of Kevin, will be hired as their new baby-sitter.

Carrie accepts Kevin's invitation to send Christmas with him and the girls. Carrie brings a homeless man, Walter, as her guest to Christmas dinner. Sometime during dinner, everyone is shocked to find Walter stole all the gifts.

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.

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 begin arguing more frequently which causes them to move into seperate rooms. They soon learn that they miss each other and move back into the same room; Kevin's doctor and Carrie begin dating and soon she thinks that Dr. Martinson wears a bra, which leads to an embarrasing moment for both Kevin and Carrie.

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.

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.