Reverend Lovejoy announces to his parishioners that Lisa is available for baby-sitting. Lisa is perplexed when no one responds to the announcement. Marge tells her daughter that people usually hire teenagers—not eight-year-olds—as baby-sitters. But Lisa’s luck changes when Ned Flanders arrives at the front door in urgent need of a sitter. Lisa’s first experience as a sitter is a success, and Flanders promises to recommend her services to everyone. Soon after, Lisa is hired by the Wiggums and the Hibberts, and her reputation grows.

Homer and Marge decide to attend the gala opening of South Street Squidport, a revitalization of Springfield’s waterfront district featuring an upscale shopping promenade. Instead of asking Grampa to look after the children, Marge and Homer allow Lisa to baby-sit her brother. Bart is shocked and outraged. He decides that if he is going to be treated like a baby, he will act like one. After Homer and Marge leave for the Squidport, Bart pours coffee ice cream down Maggie’s throat, triggering a caffeine reaction. While Lisa is distracted calming her sister, Bart combs through the phone book and places a series of crank calls. When Bart refuses to go to bed, Lisa suddenly lunges at him. Bart topples down a staircase, dislocating his right arm.

Bart locks himself inside the master bedroom and, in an effort to make his injuries appear even more serious, begins banging his head into a wall. But his scheme backfires and he knocks himself unconscious. Lisa contacts the emergency room, but an operator suspects the call is another of Bart’s pranks. Left with little choice, Lisa decides to take Bart to Dr. Nick’s clinic. She places her brother’s limp body in a wheelbarrow. But when Lisa arrives at the clinic, she discovers a long line of patients waiting to see the doctor. Lisa pushes the wheelbarrow in the direction of the hospital. Along the way, Bart falls out of the wheelbarrow and rolls down a hill. When Lisa finds his body, she realizes she is standing only yards from the Squidport gala. The townspeople look on in horror, and Lisa is labeled a “bad baby-sitter.” Nonetheless, the next day clients phone the Simpson home looking for Lisa to baby-sit.