Lisa expresses interest in babysitting, but Marge worries that she is too young. One night, Flanders urgently needs a sitter and offers Lisa the job. He gives her a glowing review, and Lisa gets steady work. Homer and Marge are so impressed that they ask her to babysit for Bart one evening while they attend the Squidport gala.

Bart is outraged that his younger sister is permitted to babysit him. After Homer and Marge leave, he feeds Maggie caffiene-rich coffee ice cream and embarks on a series of pranks that unnerve Lisa. When Bart refuses to go to bed, Lisa lunges at him, knocking him down the stairs and dislocating his arm.

To make his injuries appear more severe and get Lisa in further trouble, Bart bangs his head against a door until he is unconscious. Lisa panics and places Bart's limp body in a wheelborrow in order to transport him to Dr. Nick's clinic. However, Bart falls out and rolls down a hill, stopping only yards from the location of the gala. The townspeople are mortified, But the next day, Lisa receives even more offers for babysitting jobs.