Treehouse of Horror VII

In the kitchen, Homer lights a jack-o'-lantern but ends up lighting his arm on fire. He runs off screaming while the title, "The Simpsons Halloween Special VII" is shown on screen.

Bart and Lisa hear strange noises coming from the attic. They investigate and discover that there is a monster. Homer and Marge realize that the creature has escaped, prompting Marge to call Dr. Hibbert. He explains that Bart has an evil twin named Hugo. The two were originally conjoined but were separated at birth. Hugo was deemed too evil to live in society so they chained him in the attic, where they feed him fish-heads. Bart stays behind as the others leave to search for Hugo, but Bart realizes that Hugo never left the house. Hugo takes Bart to the attic and ties him up, so that he can reattach himself, but Hibbert returns and knocks out Hugo. He then realizes that Hugo's scar is on the wrong side, therefore Bart is technically the evil twin. To make amends for their error, Hibbert and the Simpson family sit down to a turkey dinner with Hugo, leaving Bart locked in the attic with only Hugo's fish-heads to eat.

In preparation for the school science fair, Lisa performs an experiment in a petri dish to see if cola will dissolve her baby tooth. Bart gives Lisa a static electric shock, claiming it is part of his project to prove that "nerds conduct electricity". The electric charge is then passed on to the tooth when Lisa tries to touch it, causing it to undergo an unusual reaction which creates a race of miniature beings. Lisa discovers this when inspecting the contents of the tub with a microscope, noting that their rate of evolution is accelerated. Bart destroys some of the ecosystem in Lisa's tub universe with his finger, and the tub people retaliate by sending a squadron of space ships to attack him. The inhabitants of the tub then shrink Lisa to their size with a miniaturization ray and beam her down into the tub, where they explain that they regard her as God, and Bart as the Devil. She says she can protect them from Bart if they return her to normal size, but they lack the necessary technology. Suddenly, Bart takes the tub to the science fair to the tub people's horror and submits the tiny universe as his own project, and now Lisa is forced to watch from within as Bart wins first prize.

While out fishing, Homer is abducted by Kang and Kodos. They demand that Homer take them to Earth's leader, but Homer informs them of the upcoming presidential election and says the winner could be either Bill Clinton or Bob Dole. Kang and Kodos kidnap both Dole and Clinton and place them in suspended animation, assuming their forms through "bio-duplication" to ensure that one of them will become the next leader. Before returning Homer to Earth, the aliens soak him in rum, so nobody will believe him. Most voters seem to be oblivious to the strange behaviors of Kang and Kodos in disguise, much to Homer's vexation. On the day before the election, Homer stumbles upon the badly hidden spaceship, hijacks it and releases Dole and Clinton from suspended animation. Both candidates agree they should put aside their differences and join forces to defeat the aliens and bring about a new age of bipartisanship, but Homer accidentally ejects them into space. Homer crashes the spaceship into the Capitol and unmasks the aliens, revealing the candidates' true identities to the public. However, despite being exposed, Kang and Kodos declare to the people that the two-party system means they still have to choose one of them, mocking a bystander's suggestion of voting for a third-party candidate instead. Kang is subsequently elected President of the United States, ruling as a monarchical tyrant and enslaving the American population in order to build a giant death ray.