Mary-Kate and Ashley try to convince Kevin to hire one of his new students, Carrie, as their babysitter after they get tired of Ms. Baker.
While at a slumber party, Ashley is shocked when Mary-Kate tells everyone that she has kissed a boy. Meanwhile, when Paul discovers that Carrie has been spending a lot of time at Kevin's house, rumors start to spread.
Pokey Valentine, Ashley's crush and history partner, starts spending all of his time with Mary-Kate which creates some big problems.
Mary-Kate and Ashley decide that they have to come up with a scheme to make sure that Carrie won't leave when Kevin starts dating a woman named Marci.
Mary-Kate and Ashley disobey Kevin when they switch costumes with Max and Brian in order to attend a Halloween party with Carrie that Kevin has forbid them from going to.
Carrie decides to get Mary-Kate a homing pigeon as a pet because of her bad experiences in the past with animals. Meanwhile, Ashley becomes upset after discovering that her crush, Taylor, already has a girlfriend.
Mary-Kate becomes jealous after Ashley comes home with a new friend named Nicole. Meanwhile, Carrie tries to help when Kevin and Eddie argue.
Mary-Kate is thrilled when a teen model search comes to their school, but a damper is quickly put on the whole thing when Ashley wins the photo shoot over Mar-Kate.
Mary-Kate and Ashley falsely assume that they saw their elderly neighbor, Ms. Baker, kill her boyfriend while they were spying on her through Kevin's new telescope. Meanwhile, Carrie tricks Kevin into playing the saxophone at a jazz club even though he has stage fright.
After Carrie accepts Kevin's invitation to have Christmas dinner with him and the girls, everyone is shocked to find that Walter, a homeless man that Carrie brought for dinner, has stolen all of their presents.
Mary-Kate and Ashley are making preparations to attend their first school dance, but Mary-Kate only has one goal, and that's to dance with Jeremy. But when she finds that Jeremy can only swing dance, she turns to Carrie to give her lessons.
After they begin to argue which leads to them moving to separate rooms, the girls discover just how much they really do love each other once they are separated. Meanwhile, Carrie mistakenly believes that her new boyfriend, Kevin's doctor, wears a bra.
Carrie comes up with a scheme to make her old boyfriend jealous when he comes back to town. Meanwhile, things don't go off smoothly when Mary-Kate and Ashley throw a party.
When Ashley gets a crush on Eric, a huge sports fan, but she doesn't know the first thing about sports, Mary-Kate decides to help her out. Meanwhile, after Kevin causes problems in his friendship with Carrie, he has to apologize to her.
After Kevin forgets to mail Carrie's rent and it gets her kicked out of her apartment, he has to try to find a place for her to live.
Mary-Kate's advice to Ashley on how to double the money that she raised for the school fundraiser by gambling it doesn't turn out the way she had hoped. Meanwhile, Carrie has to figure out exactly how she feels about Kevin when she begins to feel jealous after he starts to date her best friend, Nancy.
Kevin isn't happy when his brother, Matt, comes to visit because he knows that he's not able to be trusted.
Mary-Kate and Ashley find their newest class assignment of pretending to be married to be very difficult. Meanwhile, Kevin doesn't like it when Carrie starts dating his brother, Matt.
Kevin tries to find a way to politely break up with Nancy after becoming bored with their relationship. Meanwhile, Kevin and Carrie discover that the reason that Mary-Kate refused to go horseback riding when given the invitation by Carrie is because she doesn't want to remind Kevin of his wife. Also, Ashley lands herself in deep trouble after secretly making an Internet purchase with Kevin's credit card.
Mary-Kate and Ashley set up one final dinner together for Kevin and Carrie before Carrie leaves for South America for the summer.
Ashley learns a lesson in friendship when she learns that she will have to pull a mean prank on Mary-Kate's new friend to make the cheer squad. Meanwhile, Carrie and Kevin go to a ballgame together.