After suffering a mild heart attack, Grampa reveals a secret to Homer: as a young man, he had an illicit affair that produced another son. Homer sets out to find his long-lost half-brother. He learns that his sibling's name is Herb Powell and that he lives in Detroit. Homer makes contact with Herb and takes the family to Detroit. They arrive at Herb's house, discovering that he lives in a huge mansion and runs a multimillion-dollar car company.

Homer is overcome with joy that he has a wealty half-brother. Recognizing that Homer represents the typical American, Herb hires him to design a car that will appeal to middle America, thus saving his company from foreign competition. Homer sets out to design his dream car, becoming more of a hard-drive salesman than Herb. Meanwhile, Herb spends his time with Marge and the kids, becoming more of a family-man, like Homer.

Homer's car, "The Homer," is a total flop. Herb loses his business and is forced to give up all of his possessions. Loathing the day Homer came into his life, he leaves on a bus. As the Simpsons drive home, dejected, Homer is comforted by Bart, who admits that he thought Homer's car was cool.