On a boring school field trip to a box factory, Bart slips away and sneaks into Channel 6 studios, where the Krusty the Clown show is filmed. He lands himself a job as Krusty's assistant, but it is not as glamorous as he had first hoped. Just as he is about the quit, Krusty asks him to stand in for Sideshow Mel who is sick.
When Bart appears on stage, he trips over and wrecks the entire set. He utters his catchphrase, "I didn't do it!" and the audience goes wild. Bart becomes an instant celebrity, with his name on every piece of merchandise under the sun.
Fearing that it is just a fad, he tries to act intelligent, but it does not work. Eventually, he decides that he should just accept that he is a one-dimensional act, and goes out to give the best performance of his life. However, it is not funny anymore and his fame is over.