As the Simpsons approach the Kwik-E-Mart, they see Snake holding a gun on Apu. They decide it might be a better idea to shop at the Farmer’s Market. While walking through the various stands filled with fresh produce, Lisa suggests it would be healthier for everyone in the family to eat more vegetables. Marge thinks Lisa has a point, so the next time she serves dinner, it’s a vegetarian feast. All that roughage comes with a price, and before long Homer, Marge, and Bart end up taking long trips to the bathroom. Dr. Hibbert tells the Simpsons that everyone in the family consumed massive amounts of bacteria, triggering their illnesses. The only person in the family who didn’t get sick is Lisa, whose vegetarian diet helped her body build up a tolerance to bacteria. When the family returns home, Lisa sings a song, lulling them to sleep. The next day Lisa awakens to discover that everyone’s health has returned to normal. As the family watches television, Krusty the Clown announces the Li’l Starmaker Singing Competition. The winning child will appear in an Itchy and Scratchy cartoon. Bart encourages Lisa to enter the contest, telling her she has a terrific voice. Lisa is touched. That night Lisa and a long line of competitors camp out at the Springfield Mall parking lot. One by one children make their way to a courtyard stage. Krusty uses an applause meter to determine who among them will compete on air. A little girl named Clarissa Wellington wows the crowd with a fancier version of the song Lisa was about to sing. Lisa is crestfallen.

Clarissa becomes the singing competition’s first finalist. Lisa thinks there’s no way she can best Clarissa’s performance, but Homer promises to write her a great song. Homer makes his way to a music store, where he sets to work. As Lisa is about to make her way on stage, Homer runs up and hands her some sheet music. As an accompanist begins to play, Lisa sings Homer’s song. The lyrics include references to some of the townspeople. Everyone reacts with joy, and the applause meter’s needle is pushed so far it explodes, landing in Krusty’s eye. Lisa is chosen as a finalist. She tells Homer she liked working with him, and wants the relationship to continue. Later Homer speaks with a producer on Krusty’s television show about getting a specific color of light to shine on Lisa when she sings in the finals. When Homer doesn’t get what he wants, he grows enraged and beats up the producer. The taping of the Li’l Starmaker program gets underway. One of Lisa’s main competitors is a boy named Cameron, whom the audience adores. When it comes Lisa’s turn, she sings another song Homer wrote for her. The audience is moved to tears. After Lisa finishes her performance, Krusty begins eliminating challengers by pressing a remote control button, causing a little girl to fall through a trap door on the stage. Lisa’s spirits rise when Clarissa is also eliminated. Meanwhile, as Lisa’s likelihood of success increases, Homer grows increasingly abusive to everyone around him, turning into a deranged “stage mom.” Lisa grows so fed up that she fires Homer and has him escorted off the lot.

Homer is so hurt he decides to represent Lisa’s main competition, Cameron. Despite the friction between the two, Homer nonetheless gives Lisa some last minute advice before she appears on the program. This time Lisa authors her own song, and expresses what she feels in her heart. Lisa’s lyrics are filled with remorse over the professional breakup between her and Homer. Lisa tells Homer she doesn’t care if she wins or loses; she just wants him in her corner again. A short time later Lisa realizes Homer sabotaged Cameron’s appearance by writing him a song with obnoxious lyrics. The crowd boos when Cameron finishes. Lisa hugs her father.