The town of Springfield is voting for the next president, and Marge is in line. Marge calls Homer and asks him why he isn't voting. Homer is lounging on his hammock and checks his horoscope if he should vote. The horoscope says to not vote, so Homer hangs up and falls asleep. He dreams that he is voting, but hesitates about who to vote for president. Lisa asks Homer why, and if he remembers what happened in the past 4 years.

A list shows some of what Trump has done in the past few years (One of which was spelled wrong). Homer votes in his dream, but then Marge wakes him up. Homer says that it's not a big deal that he didn't vote. On January 20, 2021 (Inauguration Day), the town is in ruins with U.S. security robots all around the city. Soon the Horsemen of the Apocalypse arrive, with flags that read "pestilence", "famine", "war", and "Treehouse of Horror XXXI"!

Bart has chosen some toys to donate. Marge says he can say goodbye to his toys, and Bart says goodbye by wrecking his toys. He puts them in the box again, and gets a reward for donating the toys. Marge gives him a Radioactive Man figure, and when Bart leaves, he comes to life. Radioactive Man thinks that he s in good hands, but a Krusty the Clown doll explains that Bart tortures toys all the time. The toys in the box tell him how they ve been tortured by Bart and there s no way to stop him. Later, Bart plays with Radioactive Man and pretends that he has to save the city from a bomb. Bart puts the toy in the microwave and Radioactive Man explodes.

The toys give him a funeral and decide that they should take action. That night, the toys drag Bart to his treehouse, and they wake him up. Bart is surprised and says that he wouldn t have tortured them if he knew they had feelings. Suddenly, Milhouse comes in and Bart asks him to defend him, But Milhouse tells the toys that he isn t treated well by Bart, and he has feelings too. The toys give Bart plastic surgery and throw him out of the treehouse. Lisa discovers Bart, and realizes that he has become a pull-string toy. The family goes to Dr. Hibbert s and the doctor explains that he can t change Bart back. The toys then play with and torture Bart like he did to them, teaching him a lesson.

On Halloween night, Homer is working late at the nuclear power plant. Marge calls and asks where the Halloween candy is. Homer checks the security cameras and finds out that he ate the candy. Homer runs frantically around the plant trying to find candy, ultimately finding a strange machine with nickel slots. Homer mistakes it for a vending machine, and Homers from other dimensions come out. The Homers wreak havoc on the city, eating all the food and more, while Marge has to cook for all six of them. Lisa explains that Homer broke the space-time continuum and made Homers from other dimensions come to Earth.

Lisa says the only way is to go back to the machine and send the Homers back to their dimensions. The Homers return, but are soon interrupted by Mr. Burns and Smithers from other dimensions. After being victorious, Mr. Burns accidentally breaks the machine and everyone except the real Homer, Mr. Burns, and Smithers is sucked in. Marge then is with the homer she wants aka Detective Homer. Suddenly, he changes into Homer-Babera, who quickly leaves.

It's Lisa's 9th birthday, half way to adulthood. When she comes down to the party, Sherri and Terri makes her realize it's a party for losers, and asks for somebody to kill her, when a car comes through the window hitting her. But she suddenly wakes up back in her room, and relives the last few minutes again, having her change fate by placing Milhouse in front of the car, driven by Gil, doing his driving test with Patty. Nelson grabs her arm and brings her under Bart's treehouse, when they get crushed by it. She wakes up again at the start, getting angry and saying she can solve it, but that causes the roof to fall on her, killing her again. She this time knocks on her desk softly, but knocks the mirror on herself.

On the next return, Nelson reveals himself to be a returner too, but he falls in a woodchipper when trying to high-five her. She kills herself too upon realizing she needs to return so Nelson could live but he tells her too late that there's an alternative. More deaths happen, by being burnt by the cake's candles, to stabbing themselves with the knife, and then crushed by the air conditioner. They find out that the only way to solve the loop is to get help from Comic Book Guy. He proposes a series of solutions based on movies but they tried all of them.

In the end they find out that the only way is to kill Gil before he could crash into the house, so they throw him a brick and succeed. Lisa returns home to celebrate her birthday without consequences, except for Ralph's head being turned the opposite direction.