Lisa is selected to substitute at the Springfield High School marching band. There, she encounters
Shauna Chalmers on drums, who ignores her. Later, she finds Shauna staying late at school to practice by herself, and she admits to having a passion for music. She invites Lisa to play music at her house, but they leave for the mall when
Superintendent Chalmers interrupts them. When
Homer comes to pick up Lisa, Chalmers invites him to try the Trappist beer he brewed in his garage. Since he likes it, Chalmers volunteers to teach him how to brew it. Meanwhile, Lisa and Shauna bond at the mall. Later, Lisa begins to treat Shauna like her big sister, which worries
Marge. At Chalmers' house, he invites Homer to brew the next batch of beer by himself. Lisa encourages Shauna to try out for lead drummer. Shauna is reluctant but does it for Lisa. She impresses at the auditions and wins it. After performing at a football game, the football team quarterback, Trevor, invites Shauna to a party at his house and tells her to bring her friends. Lisa is worried about going, but Shauna says she will be with her big sister. Trevor says everyone must bring beer. As Homer finishes brewing his batch of beer, Shauna and Lisa perform to distract Homer and Chalmers while Trevor takes the case of beer that Shauna leaves outside the house. Trevor sees the rest of the beer and takes it all. At the party, Shauna deserts Lisa to be with Trevor. Chalmers and Homer find the beer missing and discover that Shauna stole it. Without Shauna, Lisa gets scared at the party and calls the police. Homer and Chalmers arrive at the party and try to collect the beer. Lisa is angry at Shauna for abandoning her, and they have an argument that ends with Lisa crying. The police arrive and arrest Homer and Chalmers for serving alcohol to minors, but the beer is nonalcoholic because Homer forgot to add yeast to it, so they are freed. Homer finds Lisa and comforts her. Later, Homer and Marge go out and have Shauna come to babysit the kids. Shauna has quit the marching band, and she credits Lisa for giving her the confidence to start her own band. They reconcile and start playing music to the annoyance of
Bart,
Maggie, and the pets. ==Cultural references==