After Bart and Lisa see Krusty the Clown do his show at the Mt. Splashmore water park on TV, they consistently irritate and supplicate Homer about going there. Homer gets annoyed, but reluctantly decides to take them there. The family goes to Mt. Splashmore, where Bart, Lisa and Homer ride an intense water slide named H2WHOA!. Due to his weight, Homer gets lodged in a section of the slide and the park's rescue crew are forced to shut down the ride and remove him with the help of a large crane. Homer is made a fool of on the news for his massive size and admits that he needs to lose weight.
Once home, Homer announces to his family that he will go on a diet and exercise more. While Homer is looking for his weights in the attic, Bart stumbles upon several old paintings of Ringo Starr that Marge made as a student in high school, when she had a crush on Starr. Marge tells Lisa that she was scolded by her art teacher for doing those paintings; she also recalls sending a painting to Starr for an "honest opinion", but she never got a response. Lisa suggests that Marge take a painting class at Springfield Community College, which she does. She makes a painting of Homer on the couch in his underwear, which her professor, Lombardo, praises. The painting wins the college art show, thus gaining her fame and the headlines of the newspapers.
Mr. Burns wants Marge to paint his portrait for the Burns Wing of the Springfield Art Museum. She reluctantly agrees, as long as Burns insists that the painting portray him as a beautiful man. While Burns heckles Marge as she does the painting, Homer finds out that he weighs 239 pounds, which is twenty-one pounds less than what it previously was. After Burns insults Homer's weight as well as Lisa and Maggie, Marge throws him out and is ready to quit until Homer encourages her to finish the painting: She also gets a reply from Starr, who is decades behind on answering his fanmail, praising her artwork. After working until well into the night, she finishes the painting and then it is unveiled at the opening of the Burns Wing. The painting depicts a naked, frail, and weak Burns. The people are shocked, until Marge explains that it depicts what Burns actually is: a vulnerable human being which will, one day, be no more. Burns is outraged at first, but then, like everyone else, accepts his new glory, praises Marge's painting and thanks Marge "for not making fun of [his] genitalia," to which Marge replies, "I thought I did."