When Milhouse gets suspended for a prank he played, Bart promises to visit him every day. However, he meets a girl named Jenny, and starts a relationship with her. Meanwhile, Lisa does a report on Springfield's future, and is sad, so Marge gets Lisa to take a happy pill, but she stops.
When Bart and Milhouse pull off a prank at Springfield Elementary, they unscrew everything in the building and watch as almost everything falls apart. Milhouse takes the fall and gets suspended from school. Homer forces Bart to sign in under Homer’s name and visit Grampa at his retirement home, and Bart soon becomes smitten with a delightful 11-year-old volunteer named Jenny (Anne Hathaway). Hoping to impress Jenny, Bart offers to volunteer at the home. He even "volunteers" to get beat up by Jimbo, Dolph and Kearney (who are being mean to a duck in order to impress Shauna) so he can save a baby duck. He invites her to his house for dinner, but as their relationship progresses, Milhouse emerges from his suspension and is less than thrilled about Bart turning his back on him for a girl. Milhouse blackmails Bart until he cracks under the pressure. He tells Jenny his real persona, and begs her to stay, because she made Bart act good for once. Jenny can't decide what to do, and breaks up with Bart. Homer then tells his heartbroken son that girls come and go, but he would always have his family.
Meanwhile, Lisa does a report on what Springfield will look like in 50 years and becomes very depressed at the dreary outlook. In class, she makes a dark speech on what will happen, horrifying her classmates and even causing one to jump out of the window screaming in terror. A concerned Marge takes Lisa to a psychiatrist who diagnoses Lisa with Environment-Related Despair and puts her on an antidepressant medication to cure her eco-blues. The drugs make her see smiley faces and Lisa nearly kiss a fan (since she saw it as a smiley face), and Marge takes her off the pills. At the Kwik-E-Mart, Lisa tells Bart that they can't hide their problems, and must face them head on. Bart agrees, and buys flowers to apologize. However, he apologizes to Milhouse, and Jenny is never seen again, because Milhouse has always been Bart's best friend. As a make-up prank, they ice the floors in Springfield Elementary, creating a massive ice rink.