In order to avoid a failing grade in gym, Lisa takes up gymnastics, which she uses to pose as a college student. Meanwhile, Bart is diagnosed with "Panda" virus and is forced to spend a week living in a plastic bubble.
Lisa can't do any sports and notices that she is failing P.E. She joins a gymnastics group taught by Coach Lugash. She gets encouragement from the ghost of John F. Kennedy in one of her dreams. Lisa notices she has perfect balance due to the encouragement from the dream and because she has a large head. Lisa starts doing extremely well in gym class. After gym she meets Tina and Carrie, two girls who she believes are just like her, eight years old and smart, only to realize that they are college students. Lisa lies to them by saying that she is a college student, too, as she wants to earn their friendship and they give her a ride home in their car and invite her to one of Robert Pinsky's poetry readings.
Meanwhile, Bart is at Krusty Burger with Grampa. He reaches in and pulls a Krusty-saurus toy out of his meal only for a mosquito from China to fly out the bottom of it and bite him and he becomes infected with the Panda Virus. To prevent it from being caught by any other people, Dr. Hibbert places Bart inside a giant plastic bubble. Bart has trouble adapting to life inside the bubble due to problems like not being able to eat and take a bath, although Homer does fill the bubble up with water and rolls it around the yard to give him a 'bath'.
Lisa thinks she is getting away with pretending to be a college student because she is going to poetry readings and night and then attending her second grade class at school in the day. While she is going to Springfield University, Milhouse, Martin and Database follow her. While Lisa is at a lecture about Itchy and Scratchy, they blow Lisa's cover and her college friends don't like her anymore. Lisa also loses her friends that are her own age because she went off with college kids.
Bart gets used to his bubble and uses it to become popular and it also amuses Homer. Bart tells Lisa that in order to get her friends back she has to pull a prank on Principal Skinner. A day later, while Superintendent Chalmers is dedicating a parking annex to Skinner, Bart rolls Lisa while she is inside his bubble. He then pushes her off the school roof and she lands on the chocolate cake next to Principal Skinner. The chocolate cake splatters all over Principal Skinner. Lisa then gets her old friends back because of this and Bart develops agorophobia because he is outside his bubble and goes to live in an air vent, only to be sucked down as the credits start to roll.