"Treehouse of Horror XV" is the fifteenth Halloween episode, airing November 7, 2004, one week after Halloween in the US. It had the lowest amount of viewers for a Treehouse of Horror episode in a few years.
In a parody of Perfect Strangers, the two aliens Kang and Kodos are preparing the Simpsons for dinner for their "boss." Bart and Homer are the main course, Lisa is in a soup, and Marge and Maggie are pies. The boss comments on the delicious meal but then vomits up Bart. For their delicous meal, Kang and Kodos get a hyper-galactic promotion. Bart is upset about being an orphan, but he is adopted by Kang and Kodos. Then The theme song from Perfect Strangers plays as the Treehouse of Horror logo appears on the screen; an alien tentacle stamps the "XV" underneath which makes it say, "Treehouse of Horror XV"
In a parody of The Dead Zone, while Trying to get his Frisbee from the roof, Homer throws a bowling ball that hits Ned on the head. When Ned recovers in Dr. Hibbert's hospital, he has a vision of the good doctor falling out of a window, which happens shortly afterwards when Homer asks him to get his frisbee from the window ledge, killing Dr. Hibbert. Ned realizes that he can see the deaths of people whom he touches; he saves Hans Moleman from falling down from a telephone line and has a vision of him getting chewed up by alligators. In shock, he drops Hans - right into an open manhole containing the said alligators, which he was standing next to. He also predicts the closing of the Rosie O' Donnell Musical theatre|musical, but he "didn't need special powers to see that one coming!"
Later, one of his visions depicts him shooting Homer. When Homer finds out about Ned's vision, he taunts him and even gives him Chief Wiggum's gun to shoot him with. Ned refrains from shooting Homer and has another vision of Homer blowing up Springfield. Ned tries to dissuade Homer from going to work saying that he'll destroy the town, and Homer promises he'll never go back... "after today, because Lenny's birthday, and they are serving ice cream cake". Ned rushes to the power plant to stop Homer who for some reason is eating the cake in the plants control center while everyone else is eating it in the staff room, his warning is scrambled by static over the intercom, leading Homer to believe he should press the "core destruct" and "kill everyone" button depsite that obviously being a stupid thing to do. In desperation, Ned grabs a nearby security guard's gun and shoots Homer; but in his death throes, Homer presses the destruct button with his tongue, causing the power plant to explode and a large chunk of central Springfield is destroyed. Homer, Marge, all the Simpsons, and the garage go to heaven as angels and they meet God who "proceeds to give Homer what is coming to him", which happens to be his frisbee.
In a parody of From Hell, taking place in 1890, London, women are being killed with swords in a series of unsolved murders. by "The Muttonchop Murderer". Scotland Yard's Inspector Wiggum challenges Master detective Eliza Simpson and her assistant Dr. Bartley easily amazed follow the swords that were bought in a shop by C. Ebenezer Burns. They find it in an opium den, where he claims he lost all his wealth to opium.
The next suspect in mind is Homer. Police arrest Homer and are about to hang him when Eliza finds the real killer: Inspector Wiggum, whose knife handle of the third body is covered by the smell of pie eels. Wiggum argues that many people like that pie, but the helper Wiggum says only that he is like eel pie and has hair in his nature. Wiggum tries to escape in a hot air balloon, which is destroyed by spacecraft Kang and Kodos. However, it turns out to be a dream that Ralph Wiggum was having while smoking opium in an opium den, which is part of a dream even crazier.
In a parody of Fantastic Voyage, at the "Invention Expo", Professor Frink creates a machine that shrinks objects. Maggie believing that it is a giant ball pit crawls inside a giant pill, which is miniaturized and swallowed by Mr. Burns. After discovering Maggie's disappearance the rest of the family agrees to be shrunk within a craft and injected into Mr. Burns' body. When Homer refuses to follow Frink's instructions, the ship gets stuck in Burns' heart. The crew puts on their swimsuits to unwedge the ship. The crew manages to get the ship free and are able to reach the stomach by catching a ride on a nerve impulse. They manage to save Maggie, but are forced to leave someone behind due to Maggie's extra body weight. The crew left Homer behind when their craft doesn't have enough power to save them all. The submarine successfully escapes, and Homer returns to his original size inside Mr. Burns' skin. Even though Homer complains that he needs several holes, Burns is confident that things will work out. And The episode ends with Mr. Burns and Homer leading a dance to the tune of I've Got You Under My Skin, with most of the whole entire cast from all three segments and the opening sequence of this episode joining in as well.