Lisa sings to the rest of the family to sleep with a rendition of "Mockingbird" (after they are all suffering from the system shock of an all-vegetable meal), which is so good that she decides to enter Krusty's "Li'l Starmaker" competition (with a grand prize of being animated into an Itchy & Scratchy cartoon). However, when another singer (voiced by American Idol's third winner, Fantasia Barrino) sings a much better version of "Mockingbird", Homer quickly pens a song about Springfield which is a hit with the crowd, and Lisa qualifies for the show. With Homer's help (especially in handling with stagehands), Lisa makes it to the finals, but when Homer goes one step too far with his stage fathering, she fires him, and he ends up lending his talents to her final competition.
After being unable to shop at the Kwik-E-Mart because it is being held up, Lisa suggests the Simpsons have an organic vegetarian meal with ingredients purchased from a nearby stall, which they enjoy until Bart, Homer, Marge, and Maggie feel queasy and begin vomiting. Later, when Bart questions why everyone but Lisa got sick, Lisa explains that they got sick because their bodies are so used to processed foods that it's a shock to their systems to eat organic foods with "vitamins, minerals and trace amounts of bug feces," which Lisa, as a vegetarian, is used to eating. As the family sits on the couch, wrapped in blankets, Lisa gives them dry toast and seltzer water, and gently sings them to sleep with the "Hush, Little Baby" song. The next morning, the family is feeling better, eating fried chicken while watching TV. They see Krusty make an endorsement for his "Li'l Starmaker" competition, a children's American Idol-style competition. The family convinces Lisa to enter, with Bart even saying that Lisa has a beautiful singing voice.
At the competition, another child (played by guest star Fantasia Barrino) sings a perfect version of Lisa's planned song, "Hush, Little Baby." Lisa starts to panic, but Homer comes to her rescue by going to the nearby music store and writing a song for her to sing. She sings the song "I'm Talking Springfield", which praises Springfield (except Ned Flanders), delighting the crowd. Soon, the competition enters its knockout stages. Homer, now Lisa's manager, starts using every means at his disposal to make Lisa feel comfortable. He even gets her the right spotlight, by beating up the technician.
The competition progresses and contestants are eliminated, leaving just fan favorites Cameron and Lisa in the final to take place the next day. However, Homer's aggressive treatment of staff at the competition makes Lisa mad, and as a result, she fires him as her manager, causing him to be upset. Later that night, as the rest of the family eat dinner, Homer enters to announce that he has become Cameron's manager. Lisa is sad that Homer is upset with her.
During the competition final, Lisa sings a song that she has written herself, called "Always My Dad," dedicated to Homer. The song expresses how much she loves her dad, and how sorry she is for hurting him. After she finishes, everyone loves it. Cameron, now restyled by Homer as "Johnny Rainbow," then goes up, and sings a rather condescending song called "Privileged Boy" that Homer wrote. The lyrics say how much better he is than the audience. Cameron is booed off the stage, with a few rotten vegetables as an accompaniment. Lisa is thrilled that Homer sabotaged Cameron in order to help her gain the prize. He tells her that he will always be there for her.