Principal Skinner closes school the day before spring break and sends the children on a "go to work with your parents day" in order to take a trip to Hong Kong because he cannot afford the $7,000 needed to fix the mistakes in his original airfare (he was assigned a window seat instead of a center seat and he specifically said he did NOT want a Kosher meal). Bart is forced to go to the DMV with his aunts Patty and Selma after Marge discovers that the project doesn't allow Bart to stay home with her, ruining his original plan. Lisa decides to go to the nuclear power plant with Homer, where she makes his workday fun and enjoyable through creative use of the hazmat suits. At the DMV, Bart makes himself a fake driver's license, which he, Nelson and Milhouse intend to use to indulge in adult activities. It goes poorly however, as they are disappointed by a showing of Naked Lunch, decide against drinking a beer at Moe's after seeing the state of the drunken patrons, and are unimpressed by Milhouse's suggestion of renting a carpet cleaner. However, spring break is saved when Martin appears, having earned $600 during his day with his father at the stock market (he originally earned over a million, but lost all but 600 when the stock plummeted), and the boys decide to use the license and the money to rent a car. The boys tell their parents they are going to attend the "National Grammar Rodeo" in Canada, but secretly take the rented car for a road trip to Knoxville, Tennessee after finding a brochure for the 1982 World's Fair. During the car ride, chaos ensues as they stop to see Nelson's favorite singer Andy Williams in Branson, and Nelson later manages to provoke an agitated father of a Canadian family traveling to Cape Canaveral to turn around and head back to Winnipeg. They also stop to pick up a drifter who looks disturbingly similar to The Hitchhiker from Texas Chainsaw Massacre and take him for ice cream.
When the boys finally arrive in Knoxville, they're disappointed to find out that the fair was held fourteen years earlier, and that its featured attraction, the Sunsphere, is now being used as a warehouse for a wig shop. The boys' car soon gets destroyed by the Sunsphere being toppled by a rock Nelson threw, and they are stranded without any transportation. On top of that, Martin spent their last $10 on an Al Gore action figure. After several failed attempts at earning money or finding alternative transportation, they sign up as couriers and then go to Hong Kong. Bart places a collect call to Lisa, who has spent the entire spring break with Homer at work, to ask her for advice. Lisa obtains Homer promise that he will not get upset and she reveals Bart's predicament. After Homer screams into his radiation suit hood, he very reluctantly agrees with Lisa that he cannot combine a rescue of Bart with murdering his lying son when he gets back to Springfield. To get Bart home, Homer contacts the Oak Ridge nuclear facility and orders a new command module for the power plant, (after spilling soda over the current one and destroying it), which ships from a courier in Knoxville with Milhouse, Nelson, and Martin stowed away inside the crate and Bart as the courier. Bart makes up a bogus story about how he found the nonexistent Grammar Rodeo to be "too commercial" as Homer and Lisa look at him with undisguised contempt and anger, while Marge looks at him with oblivious happiness to have her son back at home.
The ending credits begin with an unsuspecting Marge getting phone calls from Principal Skinner (who spotted Bart in Hong Kong), the Tennessee State Police (who inquire about the crushed rental car), and the courier office (which has an assignment for Bart to deliver a human kidney to Amsterdam). Homer snickers at these calls, which leaves Marge baffled and annoyed.