Lisa fails to solve a brain teaser that Martin, Milhouse, and Nelson easily figure out. When she then forgets her science homework and her saxophone technique, she suggests that something may be wrong. Meanwhile, Jasper freezes himself in the Kwik-E-Mart ice cream freezer, in hopes of seeing the far future. Overhearing Lisa worrying, Grampa tells her that all Simpsons start to lose their intelligence in their late childhood.

After authorities do not allow Apu to move Jasper, kids start offering to pay admission to see the frozen senior. Apu then converts the Kwik-E-Mart into a freak show. Convinced that she cannot escape genetics, Lisa surrenders to a life of stupidity.

After trying to live like Homer and Bart, Lisa becomes disgusted and storms out of the house, saying that she doesn’t want to turn out like them. Inspired by the performer at The Jazz Hole, Lisa schemes her way onto the Channel 6 newscast and pleads with Springfield to treasure their brains. Homer sees Lisa’s speech and decides to show her that all Simpsons are not stupid. He gathers all of the Simpson relatives in the tri-city area, and it’s discovered that the defective gene is only passed on to the males. At the Freak-E-Mart (formerly the Kwik-E-Mart), Jasper wakes from his hibernation, believing himself to be in the future and leaves. Losing his cash cow, Apu changes the Freak-E-Mart to the Nude-E-Mart, a strip club/convenience store.