Marge hires a nutritionist who puts Homer on a strict diet, but Homer decides to sneak in snacks and meals on the side. Marge becomes suspicious of Homer's weight gain and calls the producers of "The Sneakers," a take-off on "Cheaters." Meanwhile, Bart and Lisa go bike-riding in Springfield National Park, where they run into Martin Prince and play a prank on him. Bart and Lisa are wracked with guilt when their prank goes terribly wrong they think they're responsible for the accidental death of Martin Prince.