"Treehouse of Horror VII" is a Halloween-themed episode from the eighth season of the animated comedy series The Simpsons. It first aired in the United States on the Fox Network on October 27, 1996. Its original air date was nine days before the 1996 US presidential election, which is an essential plot element in one of the episode's segments.
In commmon with the previous Simpsons Halloween specials, "Treehouse of Horror VII" is made up of three self-contained stories; "The Thing and I", in which Bart Simpson discovers that he has an evil twin, "The Genesis Tub", in which Lisa Simpson accidentally creates a microscopic race of intelligent humanoids, and "Citizen Kang", in which the aliens Kang and Kodos determine that one of them will be the next President of the USA.
While trying to light a jack-o-lantern, Homer Simpson accidentally sets fire to his hand. The fire spreads over his body as the words "The Simpsons Halloween Special VII" appear in blood on the screen.
The Simpsons approach their couch and find the Grim Reaper sitting on it. As they near the Reaper, they collapse at his feet. He then uses their bodies as a footstool.
"The Thing and I"
Bart and Lisa Simpson hear strange noises coming from the attic. Their father Homer claims not to know what they are talking about but is seen heading towrds the attic with a bucket full of fish heads.
Later, Homer and his wife Marge are horrified when the monstrous thing they secretly keep in the attic escapes. Marge immediately contacts Dr. Hibbert, the family doctor, and asks him to come over. Dr. Hibbert explains that Bart had a conjoined twin named Hugo. The twins were successfully separated at birth but a routine soul test showed Hugo to be evil, too evil to be allowed into society. Homer explains that the family did the only humane thing they could do, they kept Hugo chained up in the attic and fed him fish heads once a month.
Dr. Hibbert and the others go out looking for Hugo. However, Hugo has not left the house. He abducts Bart and ties him up in the attic. He explains to his twin brother that he is going to sew them back together again. He tells Bart that he has been practising his surgical skills and has already succeeded in sewing a pigeon on to a rat.
Dr. Hibbert suddenly returns and knocks Hugo out. He comments that it is strange that the evil conjoined twin is always the one on the left, before seeing that Hugo's scar reveals that he was on the right and Bart is the evil one.
The segment ends with Homer, Marge, Lisa, Hugo and Dr. Hibbert enjoying a turkey dinner. Through a vent, Bart asks if he can join them. He is told to be quiet and eat his fish heads.
"The Genesis Tub"
In preparation for a Science Fair, Lisa Simpson is preparing an experiment to see if a tooth dissolves when it is kept in a petri dish full of cola. Her brother Bart is also preparing an experiment, to see if nerds conduct electricity. He uses static electricity to give his sister a shock. The electricity passes through the girl and into the petri dish. The combination of the tooth, the cola and the electricity causes a chemical reaction to occur which creates microscopic lifeforms.
Lisa observes the lifeforms frequently. Although they remain microscopic, they quickly evolve into human-like creatures and rapidly pass through all the phases of human history, soon achieving more advanced technology than modern humans. When Bart absent mindedly destroys some of the creatures' tiny buildings, they send a fleet of miniature spaceships out of the petri dish to attack him. The irritated boy vows revenge on the little beings.
The creatures in the petri dish use a shrink ray to miniaturize Lisa and bring her into their world. They tell Lisa that she is their goddess and request her help in defeating Bart. Lisa says that she can help them if she is returned to her normal size. It is explained to her that scientists have not yet found a way to do that. The microscopic Lisa is forced to watch as Bart takes first prize at the Science Fair for the petri dish full of tiny creatures.
While fishing one evening, Homer Simpson is abducted by the aliens Kang and Kodos who ask him to take them to his leader. Homer explains that the leader is currently Bill Clinton but that an election will take place in a few days time, after which the leader could be either Bill Clinton or Bob Dole. The aliens see an opportunity to begin a take over of the Earth. They will masquerade as the two candidates, one replacing Clinton and the other replacing Dole. They kidnap the real Clinton and Dole and place them in suspended animation tubes. Before they allow Homer to return home, the two aliens soak him in rum to ensure that nobody will believe his story.
On the election day, Homer finds Kang and Kodos' badly concealed spaceship and accidentally pilots it into outer space. He releases Clinton and Dole from their tubes but then accidentally ejects them into the oxygen-less void of space.
Having returned to Earth, Homer manages to unmask the two aliens in front of a vast crowd. However, the aliens are unconcerned. They say that it is now too late to find other canddates and that the United States' two party system means that people will have to vote for one of the two aliens.
Kang wins the election, enslaves the population and orders them to build a death ray aimed at his rival planet. When Marge Simpson complains about the terrible situation they are now in, Homer says that he is not to blame, telling his wife, "I voted for Kodos."