It is the last week of school before Spring Break at Springfield Elementary. Principal Skinner is planning on spending the break in Hong Kong, but he discovers that the airline has mistakenly booked him for a flight that leaves on Friday instead of Saturday. Unable to pay the huge fee that the airline would charge to change the flight date, Skinner decides to promote a "Take your kids to work day" on the Friday before Spring Break. Bart reluctantly goes to the DMV with Patty and Selma (his first choice was staying at home with Marge but finds that housewife does not count as a job since you do not get paid), Lisa goes to the nuclear power plant with Homer, Milhouse discovers the exciting world of Crackers, and Martin makes a million dollars trading commodity futures (although seconds later, he loses all but $600).
At the DMV, Bart creates a fake driver's license for himself. He, Nelson, and Milhouse are unsatisfied with its local uses, such as admitting them to see the film version of Naked Lunch, which they assumed to be pornography. They eventually decide to use some money that Martin has to rent a car and go on a road trip. As a cover story, Bart, Martin, and Milhouse tell their parents that they have been selected by their school to attend the National Grammar Rodeo in Canada. Lisa, who has never heard of such an event, can easily see through Bart's lie, but Marge only thinks that Lisa is trying to get attention. Martin and Milhouse have no problems convincing their parents. Nelson just tells his mother that he is going away for a week.
The boys rent a vehicle and head out, but soon stop when they suddenly realize they have no idea where they are going. Finding an old brochure in the glove box of the car, they decide to go to the World's Fair in Knoxville, Tennessee. But first Nelson makes them stop in Branson, Missouri (Bart: "Dad says it's just like Vegas... if it were run by Ned Flanders"), where he can see his hero, Andy Williams.
Back in Springfield, Homer asks if Lisa would like to come spend her spring break at work with him and she enjoys herself there; meanwhile, Marge becomes bored at home. Finding out that the World's Fair was over 10 years ago (the Knoxville World's Fair was held in 1982, nearly 14 years before the episode originally aired), and the aging Sunsphere has been turned into a wig shop. Bart tries to be optimistic and points out that they still have a car and a lot of money, to which Martin responds saying they don't have any more money and that he spent their last ten dollars on an Al Gore doll. Out of extreme anger Nelson throws a rock at the Sunsphere, which topples it over and destroys their car.
Now with no car, no money and nobody knowing where they really are, the boys are forced to admit that they're trapped in Tennessee. Martin maturely says that they should call their parents. But Bart, terrified of the punishment that their parents (specifically his own) would lay upon them convinces everyone to find a way to get home on their own. So, the boys go to a local pawn shop to make money. Nelson grabs Milhouse's glasses and gives them to the register. The register says that they're perfect for rebottling some antique coke bottles, but takes back the money after Milhouse blindly and accidentally knocks down and shatters all of the coke bottles. The kids try to catch a train that leads through Springfield, they succeed in tossing their luggage onto the train but fail to get on themselves (after the train out-sped them, leaving them behind without any luggage).
Bart calls Lisa and tells her the truth, which confirms her earlier suspicions. She gleefully states he will be in so much trouble when he gets home, however one story from Bart about how he's pretty much already in deep trouble convinces her to help without telling Homer or Marge. She suggests that he become a Courier as a possible way to get home. Bart manages to get a job (even with his un-laminated, unsigned license). His first job takes him to Hong Kong to deliver eyeballs, while his friends stay behind (during the trip, Principal Skinner sees Bart at the airport). After several more deliveries, Bart calls Lisa and mentions that she needs to help him find a method to have a package large enough to accommodate Martin, Milhouse and Nelson that also has a shipping destination to Springfield.
The next time Lisa meets with Homer, he notices that she seems troubled by something and asks her what's wrong. Lisa agrees to tell Homer on the agreement that he wouldn't tell anybody else (especially Bart) and she explains just what Bart has been up to. Homer's face goes a literal red with fury and he vents his displeasure by yelling into the helmet of his hazmat suit to the point that the visor completely fogged up. Homer plans to send Bart the money to get home before murdering him for lying, but is unable to otherwise he will spoil Lisa's trust in him by revealing she violated her agreement with Bart not to say anything. After some slight research about the location of Knoxville and learning that it's home to the Oak Ridge Nuclear Facility, Homer purposefully spills Buzz cola on the controls of his T-437 console and then calls the facility to order a new one in a crate. Bart forces Nelson, Milhouse, and Martin to get in the crate while flying home, and everyone knows about the trip except Marge, who receives a call from Skinner asking if Bart traveled to Hong Kong, a call asking if Bart's car was abandoned in Tennessee, and a call inquiring about Bart's availability to bring a human kidney to Amsterdam. Homer laughs. Marge asks him if he is laughing at her.