When a heat wave hits Springfield, Bart and Lisa lobby Homer for a swimming pool of their own. Homer gives in, but the moment the pool is installed, children from around Springfield invade the Simpsons' backyard. Bart attempts an ambituous dive from the roof of his treehouse. Ho loses his balance and breaks his leg.

The cast on his leg prevents Bart from enjoying the new pool and he takes refuge inside his bedroom, where he remains isolated and in darkness. Lisa realizes that Bart is lonely and bitter and gives him her telescope to help him pass the time. Using the telescope to spy on his neighbors, Bart sees Ned Flanders digging a grave in his backyard and hears him muttering about killing Maude. Bart concludes that Flanders has killed his wife.

Lisa promises to help Bart gather evidence that Flanders murdered Maude. While Flanders is away, she sneaks inside the house. Bart watches from his bedroom as Ned returns carrying an ax, and he hobbles accross the lawn to warn Lisa. Confronting Flanders, he accuses him of killing his wife. Flanders explains that the only thing he buried was Maude's favorite plant.