Thanks to the unfounded predictions of Grampa Simpson, Lisa is convinced that she's genetically predisposed to lose her intelligence. Meanwhile, Apu discovers Jasper Beardly frozen in his freezer, and turns the Kwik-E-Mart into a tourist's trap. Guest starring Phil Hartman.
Lisa tries to solve a brain teaser, and she fails as Martin, Milhouse, Bart, and even Nelson can solve it. She does not remember the code combination for her school locker, also forgets to do an agriculture project, and does a last minute job of an "eraser pig", and loses her saxophone technique. These things point to evidence that Lisa fears she is losing her gift of intelligence. When she tells about this to Grampa, he tells her that all the members of the Simpson family—including himself, Homer, and Bart—started smart at first, but later became dumber, as part of the Simpson Genes. Eventually, Lisa becomes dumb like the rest of the family, but she rejects her new-found idiocy.
She appears on Smartline and demands that the citizens of Springfield treasure their brains. As she does this, Homer brings all the Simpson family relatives to the house in an attempt to prove that the whole family is not a bunch of idiots. When all the Simpsons visit, Homer goes and asks all the men what their jobs are. These include running an unsuccessful shrimp company, shooting birds at the airport, dressing up like a millionaire and going to parties, jumping in front of cars and suing the drivers, begging celebrities for money, prison snitch and jug band manager. Lisa is even sadder, and Homer sends all of them away, beginning to feel that the Simpsons are pathetic. But then Marge says that Homer should ask the women. He finds one in a white lab coat, reads her name tag, and asks her career, "Dr.... Simpson." "I'm the chief of complicated surgeries at the invasive care clinic." Lisa finds out that all the women have great careers and that the defective gene is on the Y chromosome, so only males are affected. She regains her confidence in being smart. Bart asks if he's going to be a failure, and Homer answers that he is, Bart then seems to be depressed about it (although for just a few seconds), and Lisa solves the brain teaser that she could not solve before (which was simply numbers laterally inverted). At which point she exclaims "woo-hoo!!", before correcting herself. Proving that she is still a Simpson.
Meanwhile, Jasper visits the Kwik-E-Mart and empties all the ice cream in a walk-in cooler so he can freeze himself in that cooler and survive to see the future. Apu sees a money-making opportunity and advertising the frozen Jasper as "Frostilicus" renames the Kwik-E-Mart the Freak-E-Mart, which becomes a tourist trap. The Freak-E-Mart lasts briefly until the freezer fails, and Jasper thaws and emerges alive and well. Fearing he will lose his customers, Apu makes the Kwik-E-Mart into the Nude-E-Mart, a combination of a convenience store and a strip club.