While performing at an Easter celebration, the Springfield Elementary band members inadvertently launch hundreds of eggs from their instruments, ruining the townspeople's clothes and splattering the streets. Suspicion quickly falls on Bart, but he denies committing the prank. Lisa eventually decides that the best way to determine his guilt is to hold a trial, which is presided over by Janet Reno. The odds do not look good in Bart's favor, and he is close to being found guilty. Meanwhile, Mr. Burns rediscovers his love of superheroes after visiting Comic Book Guy's store, and he decides to become a superhero named Fruitbat Man. Smithers, fearful of Burns's safety, stages numerous crimes for his boss to thwart, using Homer, Lenny, Carl, the Crazy Cat Lady, and other citizens as patsies for supervillain identities. Desperate to find someone to solve Bart's dilemma, Lisa tries to hire Burns, but he refuses. Smithers admits to Burns all his previous exploits were faked, and this was Burns' one chance to really help someone.
As Marge washes the town's clothes, she and Lisa notice that Groundskeeper Willie's kilt is stained with only one egg, which appears to have been crushed into it by hand. Realizing that Willie is the culprit, Lisa confronts him; he confesses to committing the prank due to his hatred of the Easter holiday and shreds the kilt to destroy the evidence. As he tries to escape on his tractor, Burns intervenes and captures him, having had a change of heart. Burns turns Willie over to the court just before Reno can deliver a guilty verdict against Bart. Lisa thanks Burns and suggests that he might take advantage of his heroics to become a better person; meanwhile, Moe breaks down sobbing after he gets a phone call informing him of Bart's acquittal.
Before the end credits, there is a trailer for the "Dependables," a spoof that casts several of Springfield's elderly residents as a superhero team.