Bart swaps places with his exact double, unaware that the double’s wealthy siblings are plotting murder.

Armed with a shopping list, Homer makes his way to the Kwik-E-Mart, where Bart entertains himself by leaping from shelf to shelf. Apu tries to entice Homer into buying the last lottery ticket on a roll, which he claims is often lucky. Homer reaches for his wallet, but his attention turns to Bart, who’s performing a cannonball off a high shelf. Bart’s target, a cart of marshmallow bags, is accidentally pushed out of the way by Chief Wiggum. Homer dives to the floor, and Bart lands on Homer’s back. Moments later Lenny, who purchased the last lottery ticket on the roll from Apu, announces that he’s $50,000 richer. A furious Homer takes Bart home. Later Homer makes his way to Moe’s bar, where Lenny announces that he’s throwing a party at a posh hotel for all his friends. During the celebration Bart discovers an anteroom containing dozens of unopened gift bags for Lenny’s friends. Inside each bag is a Roomba-type vacuuming robot. Bart giggles mischievously. As Lenny swings open the door to the room, the robotic vacuums go on a rampage, converging on the guests and creating general chaos. Chief Wiggum and his men are called to the scene. Before long Bart is overheard telling one of the robots to “kill kill kill.” Wiggum knows he’s found the culprit. Marge punishes Bart by taking away his non-dice board-game privileges. A disgruntled Bart makes his way to the hotel bathroom to wash up. After downing a bunch of sweets and caffeine, he wishes aloud that he had a different family. Suddenly Bart finds himself standing next to a boy who looks and sounds just like him. Bart realizes he has an exact double.

Bart’s double introduces himself as Simon Woosterfield. Bart recognizes the name: Simon’s family not only owns the posh hotel where Lenny threw his party, they own the Woosterfield Arena as well. Simon proposes that he and Bart switch places, and live each other’s lives for a brief period. Anxious to get away from his family, Bart accepts the deal. Before they switch places, Bart and Simon tell each other about their lives. Simon says he has a butler named Chester, and two siblings: a brother, Devon; and a sister, Quenly. As Bart drives off in Simon’s limousine, he looks out the car window, and sees Homer strangling Simon. A short time later Bart arrives at the lavish mansion where the Woosterfields live. Bart is awed by the luxury surrounding him, especially when he finds football great Joe Montana hanging around the estate. Simon tries adjusting to life at the Simpsons, and is forced to dodge Homer’s food spray when Homer talks and eats simultaneously. When Simon complains, labeling Homer a “semi-literate spew monkey,” Homer sends him to his room. Lisa is puzzled by Simon’s choice of words (unaware that Simon isn’t her brother). Bart invites Milhouse to the Woosterfield mansion. Before long they encounter Devon and Quenly. Devon addresses Bart as his “half-wit half-brother.” Bart is shocked when Devon pulls a spoon out of his mouth, heats it with a lighter, and then shoves it back into Bart’s mouth. Later Bart and Simon chat by phone. At first Simon complains about Bart’s family, but his attitude changes when Marge sneaks him some pepperoni pizza. Bart, however, remains a target of Devon and Quenly’s pranks: he finds himself trapped inside a mausoleum. Burns and Smithers rescue Bart, and Bart is surprised to find that Mr. Burns treats him with great respect (the Woosterfield fortune, it turns out, is greater than Burns’). Burns tells Bart that his siblings all died in “accidents.” As a result he inherited the entire family fortune. Burns warns Bart to beware his siblings, because they could be plotting his demise. Bart realizes that Simon set him up.

Lisa grows suspicious when she discovers Simon listening to Grampa’s stories. Lisa pulls Simon aside, and demands to know what happened to her brother. Bart packs up his belongings, and prepares to leave the mansion, but Devon and Quenly remind him about their upcoming ski trip. Back at the Simpson house Lisa makes Simon tell her parents the truth. Simon says that his half-siblings are plotting to kill Bart once they reach Aspen. Homer, Marge, Lisa, and Simon drive to Aspen, where Quenly pushes Bart down a treacherous mountainside. As Bart dodges various obstacles, Homer jumps out of a ski lift in an attempt to rescue him. As Homer rolls down the mountain, he gathers snow and turns into a giant snowball. The ball overtakes Bart, who is swept inside. Eventually the giant snowball crashes into a hot tub, soaking Bart and Homer in warm water and melting the snowball. Later Aspen police arrest Devon and Quenly. Bart tells his family that he missed them.