While watching television with Homer and Bart, Lisa expresses interest in a high-tech pink diary. Later, she asks Homer and Marge to buy her the diary as a birthday present. Homer and Bart make their way to a mall to buy the diary, only to find out that the toy store has sold out of them. Homer then takes an interest in a kiosk that sells personalized videos. A demonstration video shows how, in a very unconvincing way, a friend or relative’s picture and voice can be inserted into a movie. Homer buys one of the videos for Lisa, hoping she will like it just as much as the diary. Later, Lisa opens presents at her birthday party. She thanks Bart for buying her a laser pointer, which produces a red point of light from far away. When Lisa opens Homer’s present, she tries to be a good sport when she realizes it isn’t the diary she had asked for. But when she plays the video, it becomes clear that Homer doesn’t know the first thing about her, as his “personalization” comments are completely inaccurate. Angered, she runs upstairs, sobbing.

At Moe’s bar, Homer laments that Lisa hates him because he doesn’t know the first thing about her. The barflies recommend that Homer hire Dexter Colt, a private investigator. A short time later, Homer ventures into a tough neighborhood, where he meets Colt, a hardboiled detective if there ever was one. Colt tells Homer he’ll find out everything about Lisa at a cost of $50 per day plus expenses. Colt then sets about collecting the information, and later, he presents his findings to Homer in a thick yellow envelope. Using the information, Homer is able to endear himself to Lisa by having a better understanding of her likes and dislikes. The pair travel to Springfield Labs, where they protest the unethical treatment of animals. Homer returns to Colt’s office to congratulate him on a job well done. But he reacts with shock when he sees Colt’s bill for $1000. The bill is padded with Colt’s many expenses, including a new trench coat and silver bullets. Outraged, Homer refuses to pay and runs out of the building. Later, a TV news report relays word that someone broke into the research lab and let all of the test animals escape. Evidence at the scene suggests that Lisa is the culprit. Lisa insists she was framed. A short time later, Wiggum shows up at the house to arrest Lisa. But Homer speeds away in his car with Lisa next to him.

Homer and Lisa make their way to a cabin motel, where Homer admits to Lisa that he hired a detective to find out more about her likes and dislikes. Lisa reacts with disgust. Wiggum and his men eventually pinpoint the pair’s whereabouts and raid the cabin. Homer and Lisa escape into a nearby field and run for their lives. Along the way, Homer and Lisa notice a banana in a trash can. It is full of cigarette butts. They find a big-top circus where several of the animals from the research lab are being held. Lisa realizes that Colt stole the animals and sold them to the circus. The pair turn around and discover Colt standing next to a circus cannon. Colt fires the cannon, sending the Flying Giuseppe in the stomach. He then chases Homer into the Hall of Mirrors. But Lisa uses her laser pointer to blind Colt, saving the day. Wiggum and his men arrest colt, and later, Homer tells Lisa he released the research lab animals into the wild.