A piece of tracing paper is put over a tombstone. When a hand starts going over it with black chalk, it reveals Treehouse of Horror XXXIV logo with cartoonish drawings of skeletonized Simpsons heads.

Mayor Quimby announces his decision to close an art museum and convert its art into non-fungible tokens (NFTs). After sneaking inside it, Homer inadvertently digitizes Bart into an NFT, trapped in Homer's phone. After telling Marge, she enters the blockchain to rescue Bart with the guidance of "enlightened intellects" Kylie Jenner, Rob Gronkowski and Jimmy Fallon. She appears inside a train with low-value sentient NFTs. Marge's value increases as she unintentionally destroys an NFT, consequently teleporting to the following carriage with pricier NFTs.

She kills more of them, continuing through the train before reuniting with Bart, while in the real world, Mr. Burns attempts to buy Bart as an NFT from Homer. After Marge and Bart return to the museum with Jenner's key, it's revealed that Homer turned himself into an NFT during Burns' offer. The blockchain train, driven by FOMO, runs out of fuel, rendering the NFTs, including Homer, nearly worthless.

This segment begins 30 seasons ago, as the Thompson houseboat drifts to Springfield as Sideshow Bob performs H.M.S. Pinafore for a captive audience of Bart Simpson and, having wiggled to a viewing position while still in her bindings, Lisa. But right before the last note of the finale is sung, Sideshow Bob realizes he's been played. Bart only requested this performance as a means of stalling for time. Without stalling, Sideshow Bob slices Bart apart with his machete, while Lisa watches.

Traumatized ,Lisa becomes a criminal psychology teacher thirty years later. She's called upon by Officer Nelson to help investigate a series of murders with messages of the victims' names followed by "was the first" scrawled in blood. Seeking help from Bob, Lisa rejects his offers for a riddle or anagram. At a funeral, she realizes the victims were all firstborns and traces the anagram clue to a slaughterhouse owned by Ana Gram.

Nelson is killed in the slaughterhouse. Lisa discovers security footage that portrays her as Nelson's killer in a nearby room resembling her own. The police arrest her, and Lisa reveals her split personality to Bob in a cell. "Professor Lisa" was the unaware accomplice to her crimes, and Bob's guard is her sister Maggie in disguise. Lisa executes Bob, playing the same tune he sang before killing Bart, "He is an Englishman".

At the power plant, Homer is caught eating doughnuts by Waylon Smithers. While he is complaining about society's unfair rules, a doughnut falls off and rolls, collecting nuclear waste and the DNA of assorted lab animals, but Homer runs after and eats it anyway. The donut infects Homer's DNA, creating a virus that transforms the infected into his personality and likeness and which is spread through belching. The virus spreads through Springfield and turns everyone else into Homer (including Kang and Kodos). Professor Frink takes custody of Homer's children, who are immune. They seek and find the real Homer.

Frink wishes to extract Homer's DNA to develop a cure, but he refuses, as he likes that everyone is just like he is and enjoys the lack of strict rules. Thinking he will change his mind, Frink displays an infected Marge, but Homer instead finds Marge even more beautiful than ever before. Horrified, Frink pleads with Homer about how much the world needs rules and intelligent people to enforce them.

Accepting defeat, Frink decides to call in a nuclear strike to destroy Springfield and contain the virus, but at the last second Homer accidentally tears Frink's suit and turns him into yet another Homer. The virus spreads worldwide via belching, filling the entire planet with a chorus of Homers singing "Just Like Paradise"