Bart and Lisa take Milhouse to the Springfield Aquarium for his birthday. Bart tries to clear one of the tanks with his skateboard, but his attempt at jumping the shark fails and he plunges into the water. The shark, however, is trained to carry people to safety, and Bart makes it back to land, but not without cuts to his midsection, the result of resting against the shark’s razor-sharp teeth. Marge takes Bart to the hospital only to discover that Homer has the family’s insurance card. Hibbert chains Bart to a radiator until Homer can be located. When Homer eventually shows up at the hospital, Marge demands that he buy a cell phone so she can find him should there be another emergency. Eventually Homer decides he needs a hands-free headset. He drives to an electronics store where a salesman, Armando, interests him in a device that allows all sorts of electric gadgets to be plugged into the cigarette lighter.

Before long Homer is driving around Springfield with dozens of appliances in the car. He becomes so distracted that he drives off a pier and into the ocean. A coast guard helicopter lifts Homer’s car to safety. Later, in court, Judge Harm takes away Homer’s license. When Homer laments he has no way of getting around town, Lisa suggests he take up walking. Soon after Homer is walking the sidewalks of Springfield. He temporarily jumps on Professor Frink’s Segway scooter, sending it careening out of control. Little by little Homer sees the benefits of getting where he wants to go by walking, such as losing weight and getting to work on time. The pressure of being the only driver in the family soon takes its toll on Marge, especially when she’s forced to take the kids to school after Otto trades the school bus for a guitar. Homer becomes so happy with his new walking lifestyle, he bursts into song, skipping over a large map of the western hemisphere.

When he reaches California he dances with actor Steve Buscemi. The musical number comes to a screeching halt when Homer is struck by a car. The driver, it turns out, is Marge. Marge apologizes for running Homer down with the car. She admits she saw him, but her foot went for the accelerator instead of the brake. Now, with Homer as helpless as a baby, the pressures on her have only increased. Slowly Homer recovers from the injury and begins to walk with the aid of a cane. Marge becomes upset with him and suddenly kicks the cane away. Homer topples to the ground. Marge apologizes…and realizes that, on some unconscious level, she’s trying to hurt him.

The pair make their way to a marriage counselor, who asks them both to list the names of the people whose happiness is most important. Marge places herself last; Homer puts himself first. Marge is so upset with Homer she walks out of the office. The marriage counselor tells Homer he must perform one unselfish act if he hopes to repair the relationship. One night Homer prepares an enormous dinner party for Marge, and invites people from throughout Springfield to serve Marge and express their goodwill. After Homer praises Marge with a toast in her honor, French busboys are brought in to clean up the mess. At the end of the evening a muscular Spanish man picks up Marge and Homer and carries them to the house.