The Immigration of the Body Snatchers

The Immigration of the Body Snatchers is a Bart Simpson's Treehouse of Horror story featured in.

Synopsis
Homer discovers that Springfield residents are being replaced by Pod People as part of an invasion from outer space.

Plot
Homer is taken to Springfield Mental Hospital by police, insisting that the end of the world is coming. He tells Marvin Monroe the events that have occurred:

A frightened Kearney tells Homer that his dad has been replaced by an impostor, but Homer doesn't believe him. Apu, Bart and Lisa complain that the town is too quiet. Homer gets an emergency call from Barney who shows him a giant Barney-shaped pea pod. Homer learns from a Luigi impostor that the pod is part of an alien invasion that will replace humanity with emotionless replicas as they sleep. Barney is replaced by one of the pods and he, Luigi and Chief Wiggum attempt to persuade Homer to become one of them. Homer rushes home where pod versions of Bart and Lisa try to put him to sleep. He and Marge try to escape but learn that most of the town are now pod people. They attempt to convince the others they are also pod people but when Homer excitedly consumes donuts it gives them away. After being chased they hide in a mine, but Marge falls asleep and becomes a pod person. Homer attempts to alert the press about the invasion but is run over and taken by police.

Back in the present, Homer's story is confirmed by a police discovery of pods. Dr. Monroe then reveals he is a Venusian who is also invading Earth, along with Martians, a Robot Ghost Clone from the future, giant blancmanges and apes. To make matters worse, everyone discovers they are actually characters in a comic book.