While Dave is working late, Theodore finds a little, lost kitten who came through an open window. However, the Chipmunks soon realize that Dave might not approve, as he's allergic to cats, so they decide to keep it a secret. The next morning, they argue about what to call the cat. Theodore wants to call him "Cookie," but Alvin wants to call him "Chomper." Simon breaks up the fight and decides to use both names, thus giving him the name: Cookie Chomper III. When Dave's outing is cancelled due to his allergy, his date, Roxanne, comes to the house to make dinner. During dinner, Cookie Chomper III comes downstairs and Theodore notices him under the table. They try to get him but accidentally shake the table causing Dave to look underneath. Roxanne is impressed at the sight of the little cat, and Dave decides to let the boys keep him. Simon eventually finds a cure for Dave's allergies. That night, Cookie Chomper III jumps out the window by accident and is hit by a car early the next morning. Everyone is very upset, even Alvin. Some time later, Dave tells them that they have all the great memories of Cookie Chomper III, leading into the song "Beautiful Memories." Later that day, Dave takes the Chipmunks to the animal shelter to get a new pet. Simon is initially upset by the idea, but when the puppy they choose plays with his glasses, Simon comes to accept the new puppy and love her. As they return home, Dave sneezes so Simon tries again to cure his allergy, but Dave refuses.
- This episode marks the first appearance of Lilly.
- This episode was inspired by Ross Bagdasarian, Jr. and Janice Karman's dog, Tiger Lilly. Like Cookie Chomper III, Tiger Lilly was also run over by a car and killed; The Chipmunk Adventure was dedicated to her memory.
- This episode somewhat contradicts A Dog's Best Friend Is His Chipmunk since Dave had an allergic reaction to dogs, while in this episode, he has an allergic reaction to cats. However, oddly enough, Dave develops an allergic reaction to dogs near the end of this episode.
- During the dinner with Roxanne, Simon is wearing a white jacket and tie, but at a closeup of the Chipmunks saying "Can we keep him?" he is wearing his ordinary blue sweater.
- This episode is apart of the Alvin's Thanksgiving Celebration and Driving Dave Crazier DVDs.