Bart's class takes a field trip to a local box factory. Bored, Bart sneaks away to the nearby television studio where "The Krusty the Clown Show" is taped. After Krust fires his intern for not supplying him with a Danish, Bart steals a pastry from Kent Brocknman and brings it back to Krusty. The grateful Clown hires Bart as his new assistant.

Working for Krusty is not what Bart expected. Just as he is about to quit, Krusty offers him a one-line bit part in a comedy sketch. Bart accepts. While on stage he trips over a prop and causes a near disaster uttering, "I didn't do it." The audience goes wild, and Bart becomes an instant celebrity.

With, "I didn't do it" as his catch phrase, Bart's image appears on numerous products. He appears on "Late Night with Conan O'Brian" to prove that he is not just a fad. Bart tries to give his best performance on an upcoming episode of Krusty's show, but when his moment comes, no one laughs. Krusty explains that his stardom has ended, attributing it to the fickle nature of show business.