Bart becomes addicted to junk food when a new vending machine is installed at Springfield Elementary. His steady diet of processed foods leads to a massive weight gain and health issues. When he's unable to stick to his prescribed low-fat diet, the Simpsons stage an intervention and ship Bart off to "Serenity Ranch - A Forced Starvation Facility," headed up by former food addict Tab Spangler. While Spangler tries to help Bart overcome his obsession, Homer and Marge turn their home into a hostel for German travelers in order to pay for the costly Serenity Ranch.

An apocalyptic movie followed by three real-life omens cause a fearful Homer to research the rapture. Believing that he has deduced when the event will happen, he begins warning others as a way to secure his spot in heaven. After a skeptical Kent Brockman reports on Homer's prediction of stars falling from the sky, there's a Krusty Special blimp accident, and Homer attracts a slew of new believers. When the rapture never comes, a discredited Homer discovers an error in his calculations and returns to the Springfield Mesa alone, where he experiences the rapture - or maybe a heat-induced dream - and convinces God to delay doomsday.