The boys disobey Dave and instead of seeing a kid's movie, they go in and see a horror movie. The movie ends up scaring the Chipmunks out of their wits. All night, the boys think that Hideous Harold, the creature from the horror film, is after them.

Theodore encounters a stray kitten that entered through an open window in the house. He and the boys take an instant liking to the kitten, and after some compromising, they name the kitten Cookie Chomper III, and after Dave is cured of his allergy to cats, he comes to like the kitten as well. After Cookie Chomper gets run over, the boys have a hard time dealing with it. Eventually, they get a new pet, a puppy they name Lilly.

The Chipettes are excited for the summer holidays, but not when Miss Miller keeps making other plans for them. The girls decide to hook her up with an elderly man by the name of Mr. Flowers.

Dave gets a bump on the head and forgets who he is. After seeing a commercial, Dave becomes a trendy stylish man.

Alvin is tired of being treated like a kid and trades place with Dave for a day to feel what it is like to be a grown-up.

The Chipmunks overhear Dave suggesting that he would prefer Alvin to be a Gymnastic Pizza Twirler, Simon a Pogo Stick Tester, and Theodore an iguana trainer, and immediately start to pursue those careers.

Brittany tries to join the cool kids at school.

Alvin tampers with Simon's hair growth formula and instead having it grow Simon's hair, it turns him into a heartthrob.

Alvin is desperate to write an essay on George Washington, that he uses Simon's time machine to bring George into the future.

Alvin has a dream that he is a detective from the 40s. He is on a case to find a famous rich girl named Brittany.

Theodore goes on a diet so he could go on a date with a pen pal, who is also one of Alvin's biggest fans. Things go wrong when Alvin finds out that Theodore's date is actually the daughter of a famous film director. Alvin then takes her out instead, breaking Theodore's heart. In order for Alvin to make it to his play and the date, Alvin gets Theodore to switch back and forth to his play and on his date.

Brittany makes a bet with Missy Snootson, another girl in her class, that if the mummy of king Rooten Tooten does not rise from the dead and go to her home by midnight, Brittany must drop out of the race to be the school Carnival Queen.

After years of scrimping and saving, Dave is finally able to afford their own vacation cabin. Alvin hears that Robby Leach, the host of the show “Lifestyles of the Truly Fabulous” lives nearby. Alvin tries to get Leach to interview him, and at the same time he makes a few quick changes to Dave's cabin.

Alvin lies to his classmates that he will be singing on stage with Michael Jackson. As Alvin tries to find Michael in order to see if it really is possible he could perform with him, he meets up with the big star's manager. To Alvin's surprise, this so-called manager is a homeless man looking to find a place to stay.

The Chipettes decide to quell Miss Miller's losing streak at poker with her girlfriends by secretly helping her cheat, which eventually leads her to Las Vegas, with the Chipettes in tow.

When the Chipettes are discovered to be living alone, Dave must find a supervisor for them.

Brittany attempts to market her own perfume.

Alvin "borrows" Dave's new bike, and while he is out riding he accidentally hits Brittany who is out roller skating. The bike is ruined, and something is wrong with her skates. They each blame each other, and Alvin demands Brittany pay for Dave's bike, while she insists he pay for her roller skates. All of this brings us to court, where Brittany and Alvin, ignoring the "TRUTH" part in justice, face off in a "who can tell a better lie about what happened" court battle.

Alvin goes through an identity crisis and starts trying all kinds of different personalities, with embarrassing results.

The Chipettes discover the joys of writing in a diary. Tension builds between them when they deliberately sneak a peak at what the other Chipette has written.

Dave, the Chipmunks and the Chipettes go to Washington D.C. to lobby the president to save bald eagles.

Simon feels unappreciated and stows away on a cargo ship.

Alvin becomes jealous when Simon becomes a celebrity in Australia.

Alvin plagiarizes his book reports and Theodore is on the council that will judge him.

The boys have to paint the garage after they got spray paint on the walls while repainting their bicycles. Simon and Theodore feels bad because they always have problems with Alvin's ideas. Later Alvin have them to go to a mansion of a now dead criminal. Alvin is convinced that a never found loot from a bankrobbery is still hidden there. They go because Alvin promises to paint all the garage if he's wrong, but they feel a little bad with Alvin.