Homer experiences a mid-life crisis when he realizes, at 38.1 years of age, that he hasn't accomplished anything meaningful. To curb his remorse, Homer decides to pattern himself after Thomas Edison and become the next great inventor.
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 years old, his life is half over. When he tells Marge this, she informs him that he is actually 39. Homer realizes that with time running out on his life, he hasn't accomplished anything, and this causes him to fall into a severe depression. Later when the family has a party to honor him, Lisa mentions that Thomas Edison invented the film projector as well as many other inventions Homer uses. Homer learns more about Edison and eventually idolises him. And so in an attempt to follow in Edison's footsteps, he quits his job at the power plant to become an inventor.
Homer gets to work and develops several inventions, such as an alarm that beeps every three seconds when everything is OK, a shotgun which shoots make-up onto women's faces, a very difficult to control electric hammer, and a reclining chair which has a built-in toilet. But none of these inventions is well received. Feeling despondent over his failure to invent anything useful, his invention career is saved when he reveals he added two hinged legs to a chair making it impossible to tip over backwards. However, his hopes are dashed when he notices his poster of Edison shows his idol sitting in the same type of chair, which indicates Edison has already invented Homer's untipable chair. But Homer also finds out no one else has seen the extra legs on Edison's chair, and thus Edison has never received public credit for inventing it. So he sets out with Bart and his electric hammer to the Edison Museum in New Jersey to destroy the chair. Before he smashes the chair, Homer notices a poster of Edison's which reveals that Edison idolized Leonardo da Vinci in the same way Homer idolizes Edison. It also shows that Edison was never able to match da Vinci's accomplishments, just as Homer can not match Edison's. Feeling a renewed connection to his hero Edison, Homer decides not to destroy the chair after all.
The next day on the news, Kent Brockman announces that the chair has been discovered, along with Homer's electric hammer which he accidentally left behind. These two patents are expected to generate millions for Edison's already wealthy heirs. As Lisa says that the money should be Homer's, Bart says to him "Wow, Dad, I have to say, you're taking this rather well." Through gritted teeth, Homer replies "Let's just say I'm sitting in the right chair", his Lazy Man Toilet Seat.