Bart discovers his Siamese twin in the attic; Lisa becomes a God after she accidentally creates life in a science fair project; Kang and Kodos plot to conquer the planet.
In "The Thing and I," Bart hears something in the attic one night and his parents tell him that it's his conjoined twin brother, Hugo. Hibbert then reveals that there was an irregularity when he was born and one of the twins was pure evil. Marge and Homer then locked Hugo in the attic and fed him a bucket of fish heads once a week. When Hugo tries to sew him and Bart back together, but Hibbert reveals that Bart was always the evil twin. In "The Genesis Tub," Lisa accidentally creates a rapidly evolving universe in a small tub. This new race calls Lisa a God and Bart the Devil after he attacks. Lisa is brought down to the race's size and is therefore unable to help her people. In "Citizen Kang," Kang and Kodos abduct Homer and tells the aliens of a presidential election after being asked for their leader. The aliens then steal the identity of Bill Clinton and Bob Dole to be elected and take over Earth. Homer tries to get the real guys back, but accidentally kills them. When he gets back, he reveals Kang and Kodos' true identities, but they still take over Earth.
- "The Thing and I"
Bart and Lisa both notice their parents acting a little strangely, notably taking buckets of fish heads into the attic, and even hearing strange noises as well.
Out of curiosity, they go up into the attic, only to see a shadowy figure rush down the attic ladder, and out of the house.
It is then that Homer and Marge (along with Dr Hibbert, who conveniently stopped by), tell that Bart was born as a conjoined twin. However, it was soon found out that the twin (named Hugo), was found to be evil. While Bart was considered the good twin, Hugo was confined to the attic, and fed fish heads once a week.
The rest of the family goes out to find Hugo, leaving Bart at home. However, it soon appears that Hugo didn't leave, and straps down Bart, intending to stitch him and Hugo back together. Though Bart claims that this will kill them both, Hugo claims that being stitched back together will make him sane.
However, the others arrive in time to stop Hugo, but find out that Hugo's scar from the separation years ago is on the wrong side...and the real evil twin, has always been Bart.
The family then decides to resolve the issue, by letting Hugo live a normal life, and putting Bart in the attic.
"The Genesis Tub"
Lisa attempts to create a science project to show how soft drinks rot away teeth. Using a baby tooth, she puts it in a small 'tub' of cola. Bart comes by, and shocks Lisa with static electricity, and when she reaches for the tooth, a spark from the static arcs onto the tooth.
The next day, mold has formed in the tub, but upon analyzing it closer, she finds that there are tiny people living in the tub. Over the course of several hours, the people evolve through the Renaissance, and into a futuristic society.
When Bart finds out about this, he pokes the dish several times, destroying parts of the city.
In the night, the little people launch an aerial attack on Bart, before returning to the tub. Lisa prevents Bart from getting revenge, but he promises that he will get back at them.
As Lisa wonders what to do next, a strange ray envelopes her, and shrinks her down into the tub. Having been shrunken by the 'de-bigulator,' Lisa is revered as a god by the tub people, who wish her to save them from 'the devil,' aka Bart.
Many in the tub wish Lisa to solve their problems, but she claims she can do so if she's returned to normal size. However, just then, Bart appears overhead, and seals off the tub.
When the lid he put on is taken off, it becomes apparent he has entered the tub in the science fair, with Principal Skinner claiming Bart's miniature world is the first prize winner.
Lisa yells that she should be rewarded, but she's too small to be heard. Realizing she's trapped in the tub forever, she takes to task the appointment of being the little people's ruler, demanding they grovel, and fetch her shoes.
While out fishin, Homer is abducted by Kang, and his sister Kodos. They demand Homer take them to 'his leader.' Homer claims that Bill Clinton is the current leader, but with an impending election, Bob Dole could become the new leader.
Kang and Kodos then capture both Clinton and Dole, and assume their form. To keep Homer from telling what he's seen, they spray him with rum, and kick him out of their spaceship.
Kang and Kodos continue the election campaigning, with Homer's truth falling on deaf ears. He does find their spaceship, and attempts to get Clinton and Dole back to Washington. On the trip, both of the men find common ground, and decide to work together. However, this is thrown out of whack when Homer ejects them into space.
Homer then crashes the ship into the Capitol, before rushing out, and finally exposing Kang and Kodos for what they are.
The two admit to being aliens, but since they are on the ballot, the public still has to vote for one of them. Someone mentions that the only way around this is to vote Independent, but the aliens laugh, as this would be akin to 'throwing a vote away.'
In the end, Kang is elected, and the human race is enslaved. Homer claims that he can't be blamed, as he voted for Kodos instead.