Homer's silhouette appears next to Alfred Hitchcock's iconic silhouette. He emerges and warns viewers that the following episode could scare certain viewers especially religious types as he believes, an announcement mirroring to what Marge did in the beginning of Treehouse of Horror and Treehouse of Horror II, warning viewers. He requests for the television to be turned off before daring viewers imitating a chicken. The TV screen eventually switches off, however, Homer and Marge could still be heard if not seen. The episode then pans to a cemetery and eventually to the Simpsons house, with the family in their couch gag as skeletons.
The Simpsons are having a Halloween party, and they tell scary stories. The Halloween costumes include Homer as Julius Caesar, Marge as an ancient Egyptian, most likely Cleopatra, Bart as Alex DeLarge from A Clockwork Orange, Lisa as the Statue of Liberty, Milhouse as Radioactive Man, Martin as Calliope, Nelson as a pirate, Janey as a princess, Wendell as an astronaut Lewis as Frankenstein's Monster Richard as Scratchy. and Ned Flanders as a headless zombie.
After forgetting to buy him a gift for his birthday, Homer buys Bart a talking Krusty doll at 'House of Evil' (your one-stop Evil gift shop) which also sells frozen yogurt called frogurt. Upon receiving the Krusty doll, Bart excitedly says "Great Caesar's ghost!", a catchphrase said by Perry White of the Superman comic book series. Although the doll is nice to Bart, it repeatedly tries to kill Homer (which no one believes). Homer captures the evil Krusty in a bag of dirty socks, which he then locks in a suitcase. He disposes of the suitcase in a "Bottomless Pit" and returns home, not realizing that the doll has managed to follow him. As the doll attempts to strangle Homer, Marge calls KrustyCo for help; a repairman arrives and discovers that the doll has been accidentally switched from "Good" to "Evil." He flips the switch back to "Good" and Homer uses the doll as a servant. The Krusty doll laments to his "girlfriend" Malibu Stacy, with whom he shares Lisa's doll house, "Today Homer made me give him a sponge bath!" However, the scene ends happily as Krusty gives Stacy a smooch on the cheek—until her head falls off.
This a parody of the Twilight Zone episode, Living Doll.
In a black and white segment which is a parody of King Kong, Marge joins Mr. Burns and Smithers on an expedition to "Ape Island" to find the legendary "King Homer". Mr. Burns captures the giant ape and displays him to the press on Broadway. The photographers' flashes enrage King Homer, who breaks free from his restraints. He abducts Marge and wreaks havoc, eating many people in the process. He attempts to climb a tall building, but is unable to get even one story above the ground. King Homer collapses in exhaustion, and Marge helpfully suggests that he eat more vegetables and less people. In the end, King Homer and Marge marry on the same day Dick Cavett is born (November 19, 1936). The story ends with the wedding, and King Homer eating Marge's father Clancy Bouvier, although Marge is brave and not upset.
While in the school's library searching for material for a book report, Bart finds a book of magic in the occult section. In order to make Lisa happy, he tries to resurrect Snowball I for her, but accidentally reanimates hundreds of human corpses instead. The zombies terrorize Springfield, turning several people, including Principal Skinner, Ned Flanders, Krusty the Clown, Sideshow Mel, Edna Krabappel, and the bullies, into zombies. Meanwhile, the Simpson family has barricaded all the doors and windows except for the back door, which Homer completely forgot to do because he was watching TV. Several zombies break into the house: Homer sacrifices himself to give the others time to escape, but the zombies leave him when they realize he does not have enough brains for them to eat. Lisa realizes that the school library must have a book that can reverse the spell. The family runs to the car under the protection of Homer’s shotgun. Flanders comes over and asks, "Mind if I chew your ear?" Homer responds by blasting Flanders with his shotgun. The family voice their shock that he killed the zombie Flanders, to which Homer responds “He was a zombie?" Meanwhile, the Simpsons arrive at Springfield Elementary and burst through the doors until Homer wields a shotgun to kill the famous zombies including George Washington, Albert Einstein, and William Shakespeare. Later Bart and Lisa find the book in order to reverse the spell in the Springfield Elementary library. Bart successfully finds the book and casts the spell—that accidentally turns Lisa into a snail, shocking him. Lisa doesn't notice her transformation and asks Bart what, he replies,"I just haven't noticed what a beautiful, young woman you're becoming," flattering her. Bart finds the correct spell and casts it upon the world, returning the zombies who were dead before the spell to their graves, those who became zombies by infection drop dead in the streets and turning Lisa, who had been unaware of her change, back to normal. In the end, the family ends up back at home on the couch watching TV, just before the credits roll in.