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.