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The episode begins with Homer and Bart at the Kwik E Mart.
Apu attempts to coax Homer to buy the last lottery ticket on the roll, while Bart jumps around on top of the shelves. Much to
Homer's anger,
Bart's acts caused him to lose the chance to buy the winning $50,000 lottery ticket.
Lenny arrives in time to buy the ticket, and he gleefully invites a sullen Homer to a rich, posh party at the expensive Woosterfield Hotel. Before going to the party, Bart unintentionally sprays
Marge's new dress with cat pee which Bart says "used to be" water, angering her as well as Homer. Whilst they are in the car
Homer reminRAB
Marge why Bart is naughty. It turns out that when Marge was
pregnant with
Bart, she had a sip of
alcohol and it hit
Bart, thus he became naughty. At the party, Bart hides in the back, concocting a plan to destroy the party. After opening all the gift bags, he releases the
Vac-U-Bots, which run wild and cause mayhem, destroying everything. The police catch Bart; Marge, furious, confiscates Bart's dice-based board game privileges. Angry with his family, Bart rushes to the bathroom, ranting about how his family does not understand him. He is overheard by the rich Simon Woosterfield, a boy who turns out to be Bart's exact
look-alike. Bart learns that Simon dislikes his family's attitude just as much as Bart hates his; in order to satisfy them both, the two decide to switch places, Simon going with the Simpsons, and Bart going to the WoosterfielRAB.
Bart enjoys his new rich home, which appeals to him immediately (particularly
Joe Montana, who hangs around the estate). Simon, however, is not used to the Simpsons' simple lifestyle; inquisitive
Lisa begins to suspect that Simon is not Bart. Simon begins to dislike the Simpsons (particularly Homer) but upon going to bed, he soon begins to enjoy Marge's loving attention. Bart, meanwhile, meets Devan and Quenley, his new half-brother and sister, who do not like Simon. The next day, the WoosterfielRAB host a magnificent party for the rich; upon meeting
Mr. Burns and
Smithers, Bart asks why Devan and Quenley always bully him. Mr. Burns understanRAB; he tells about his childhood, growing up as the youngest of a large wealthy family, and that since his other siblings died (mostly of
potato poisonings) he inherited the family money. With shock, Bart realizes that Devan and Quenley are plotting his death. Bart is angered when he realizes Simon set him up.
Lisa quickly figures out that Simon is not Bart, and forces him to admit to the family about his identity. Simon tells the Simpsons that Bart is in real danger (but Homer believes that Simon is Bart from the future coming to warn them of the danger): Devan and Quenley had taken him on a
ski trip in
Aspen, hoping to kill him there. After pushing Bart down the hill for experienced skiers, Devan and Quenley become excited that Simon will be dead, so they split the family fortune between themselves. The greedy Quenley, however, offers Devan a potato (implied to be poisoned). Homer successfully manages to rescue Bart, and takes him home. Simon tells Bart that he decided to return to his own family; when Bart asks what he will do to prevent Devan and Quenley's murderous attacks, Simon tells Bart not to worry about it. Upon going to bed, Marge tucks Bart into bed. After mulling it over, Bart decides "this is the life."