When Homer and Marge's marriage declines due to their fading sex life, Abe pieces together a medication|tonic that is guaranteed to put the sparks back into their relationship. The effectiveness of the tonic results in Homer and Abe going into business together, selling "Simpson and Son’s Revitalizing Tonic" to the public utilizing a medicine show. They travel from town to town selling the product, but after visiting the farmhouse where Homer grew up, the two get into an argument. Abe yells at Homer in the car, saying that if he had not taken the tonic years ago, Homer would not have been born, finally shouting "You were an accident!" Homer stops the car and hisses "Get out!", not accepting Abe's apology and saying in an "OUT". Abe steps out of the car and says he hopes Homer will forgive him, but Homer drives away and leaves his father there, later telling Marge he cannot forgive what his father said and then resolves to be a better father. However, things don't go well for either Homer or Abe: Homer's rushed efforts to bond with Bart and Lisa lead them to note that he's just as "half-assed" at doing too much as he was at being a non-presence for them, while Abe's attempt to use Barney as the new "Son" fails instantly.
Bart attempts to figure out why all of the adults disappear after they buy the "Simpson and Son's Tonic". They come up with a few conspiracy theories, all of which are unrelated with the tonic. Lisa, however, offers up the possibility of all the adults having to be home before dark, which frightens the rest of the children more than their other ideas.
Depressed at having failed to be a good father even when he is trying, Homer goes back to the farmhouse to think. He sees old photographs, including one of himself as a child on Christmas morning, where he thinks his father was not even there on Christmas when he finally got to meet Santa Claus. Homer then realizes that it was really his father in a Santa costume, proving that Abe did actually care for him. Homer quickly reunites with Abe, who by coincidence has also gone to the farmhouse to reflect. Both of them accidentally set fire to different parts of the building, starting with Homer accidentally setting fire to the photo and Abe throwing a bottle of his tonic into a fireplace at the end, and bump into one another on the front porch while fleeing the blaze. They both admit they are screw-ups and they finally reconcile.