Marge grows concerned that her marriage is in trouble when Homer stops having the urge to make love to her. She and Homer visit a local bookstore where they purchase a book-on-tape called "Mr. and Mrs. Erotic American" by Paul Harvey. Despite their attempts to follow the tape’s advice, Marge and Homer’s sex life remains nonexistent. Grampa senses that the couple’s marriage is in deep trouble. He concocts a home remedy that he guarantees will put sparks back into the relationship. Skeptical, Homer takes a swig. He immediately runs home and makes love to Marge.

Marge suggests that Homer and his father go into business together and sell the tonic to the public. With Grampa acting as pitchman, sales for the tonic skyrocket. The pair take to the road, selling the tonic from town to town. But Homer grows irritated with his father’s annoying personality. During the trip Grampa takes Homer for a tour of a farmhouse where they once lived. Homer accuses his father of never giving him any encouragement-even when he was a child. Grampa tells Homer that his conception was an accident. Incredibly hurt, Homer kicks Grampa out of the car.

At first, Homer rejects his father’s plea for forgiveness. Homer decides that, unlike his father, he will show his children the attention they deserve. But he overcompensates for years of indifference. Bart and Lisa tell their father they were better off without so much attention. Homer returns to the farmhouse and discovers an old photograph of his father dressed as Santa. He realizes his father did care about him after all. Homer and Grampa accidentally set fire to the farmhouse. They both admit they are "screw-ups."