When Lisa has difficulty performing exercises during gym class, her teacher, Mrs. Pommelhorst, gives her a check-minus grade. Skinner sees this and immediately protests, as Lisa is single-handedly keeping the school accredited. Mrs. Pommelhorst decides that the best course of action is to place Lisa in the hands of Lugash, a Romania coach obsessed with gymnastics. As Lisa trains, she bumps her head…and soon experiences a hallucination involving John F. Kennedy. Kennedy, who created the President’s Council on Physical Fitness, encourages Lisa to train her body. Her spirits lifted, Lisa approaches the gymnastics exercises with new vigor, winning praise from Lugash. Inside the locker room, Lisa befriends two fellow gymnasts—Carrie and Tina. Lisa notices that the girls are extremely intelligent…and soon realizes they’re both college students. Lisa is overjoyed when they offer her a ride back to campus. Pretending she’s also a college student, Lisa accepts their offer.

Meanwhile, Grampa takes Bart to a Krustyburger fast food restaurant, where Bart receives a Krusty-saurus plastic toy giveaway. Bart notices a buzzing sound coming from within the toy, and when he investigates, is bitten by a mosquito that became trapped inside the toy during the manufacturing process in China. Bart soon falls ill. Dr. Hibbert realizes Bart is suffering from Panda Virus, and as a precautionary measure the boy is confined to a plastic bubble. Meanwhile, an overjoyed Lisa continues hanging out with Carrie and Tina,and accompanies them to a coffee house where poet laureate Robert Pinsky reads from his works. After the reading, Lisa realizes she forgot about an elementary school assignment due the next morning. She rushes home and constructs a miniature version of the White House using matchsticks. But when she brings it to school, one of the matches accidentally ignites, setting the project ablaze. Still, Miss Hoover awards her an A-minus, as the project, despite its state, is still the best in the class.

Meanwhile, Bart happens upon Jimbo, Dolph and Kearney as they harass some fellow students. He uses the protective plastic bubble as a defense shield and successfully overpowers the bullies. Later, Milhouse, Martin and Database notice Lisa behaving in an unusual manner. They decide to spy on her. Lisa makes her way to a college lecture hall, where a young, hip professor is giving a lecture on Itchy and Scratchy cartoons. He screens one of the cartoons for the class, and when the lights come up, he notices Milhouse and his friends lying on the floor. When the professor notes that children aren’t allowed in class, Milhouse points to Lisa and states that she’s eight-years-old. The professor asks an embarrassed and disappointed Lisa to leave.

As Lisa’s spirits fade, she happens upon her father, who has turned his attention to a tree. Homer sheepishly explains that he had attempted to throw Bart over the roof of the house, and in the process, Bart got stuck in a tree. Lisa uses her gymnastic skills to move up the branches. When she finds her brother, she puts her arm around the bubble and expresses sympathy for him. But Bart tells her that the bubble has made him more popular than ever. Lisa tells Bart that she wishes she could trade places with him. Bart comes up with a plan that will allow Lisa to win back her old friends.

Later, at the elementary school, Principal Skinner, clad in a clean white suit, is honored during “Seymour Skinner Day.” When one of the students asks Skinner to pose next to a celebratory cake, Skinner is more than happy to do so. At that moment, Bart pushes the plastic bubble—which now contains Lisa—along the roof of the elementary school. Bart pushes the bubble off the roof, sending it and a complicit Lisa into the cake, which splatters all over Skinner’s clean suit. Overjoyed students grab Lisa and put her on their shoulders.