Homer is shocked to hear on the radio that the average life expectancy for men is now 76.2 years, which makes him realize that, at 38.1, his life is half over. Marge informs him that he is actually 39, which depresses him even more. Homer thinks he has not accomplished anything that will be considered worthwhile after he dies. His family tries to cheer him up by showing him a film of his accomplishments and a special appearance by the character KITT from the Knight Rider television series that Homer is a fan of. When the film projector stops working, Lisa mentions that Thomas Edison invented the projector as well as many other inventions. Homer decides to learn more about Edison and eventually idolizes him. He becomes so obsessed with him that he unknowingly begins to annoy people with stories about Edison's life and inventions. In an attempt to follow in Edison's footsteps, Homer quits his job at the power plant to become an inventor.
Homer gets to work and develops a few inventions, such as an alarm that beeps every three seconds when everything is alright, a shotgun which shoots make-up onto women's faces, an electric hammer, and a reclining chair which has a built-in toilet. None of these inventions are well received by his family and he feels disappointed over his failure to invent anything useful. However, he soon becomes encouraged when he discovers that the family likes one of his other inventions – a chair with two hinged legs on the back, making it impossible to tip over backwards. His hopes are destroyed when he notices his poster of Edison, which shows Edison sitting in the same type of chair, indicating that he has already invented Homer's untippable chair. Bart points out that the chair is not featured on a list of Edison's inventions, and that maybe no one knows he invented it.
Homer and Bart therefore set out to the Thomas Edison National Historical Park in West Orange, New Jersey with his electric hammer to destroy the chair. Before he smashes the chair, Homer notices a poster of Edison's which shows he had fewer inventions than Leonardo da Vinci. This means that Edison compared himself to Leonardo, much like Homer compares himself to Edison. Feeling a renewed connection to Edison, Homer decides not to destroy the chair. Homer also suggests that they destroy some of Leonardo's creations, but when Bart points out those are in Italy, Homer settles for taking it out on Eli Whitney.
Homer and Bart return to Springfield, without knowing that they left Homer's electric hammer behind at the museum. Later when the family watches the news on television, Kent Brockman announces that the chair and the electric hammer have just been discovered at the Edison Museum and are expected to generate millions for Edison's already wealthy heirs. After Lisa complains that it should have been Homer's money, Homer angrily comments that it is a good thing he is sitting on his reclining toilet chair.