Marge and Homer's sex life becomes non-existent, and sensing that the couple's marriage is in deep trouble, Grampa concocts a home remedy that he guarantees will put sparks back into the relationship. Homer is skeptical but takes a swig. He immediately runs home to make love to Marge.

At Marge's suggestion, Homer and Grampa go into business together and sell the tonic from town to town. During one outing, they visit the farmhouse where Homer grew up and have a disagreement. Homer accuses his father of never encouraging him, while Grampa tells Homer that his conception was an accident. Incredibly hurt, Homer kicks Grampa out of the car.

Homer vows to show his children the attention they deserve, but he overcompensates. Bart and Lisa tell him that they were better off without so much attention. Homer and Grampa each return separately to the farmhouse. Homer discovers an old photo of his father dressed as Santa. He realizes that his father did care about him after all. Accidentally setting fire to the farmhouse, Homer and Grampa admit that they are "screw-ups."