After watching an advertisement on television for Duff Gardens, Homer, Bart and Lisa decide to go. As they prepare to leave, Marge tells them that spinster Great Aunt Gladys died and they will be going to her funeral instead. The Simpsons, along with Patty and Selma, drive to Littleneck Falls to attend her funeral and the reading of her will. On the video will, Great Aunt Gladys tells Patty and Selma not to die alone, as she did. Selma hears the ticking of her biological clock, and decides she wants a child. Selma tries video dating, but gets rejected by Groundskeeper Willie. She goes to a psychic who tries to sell her a love potion. The psychic ingests it, blurts out the innocuous ingredients and discovers that she accidentally drank a truth serum. Selma dates Hans Moleman after revoking his license at the DMV. All goes well until Hans tries to kiss her goodnight; Selma envisions herself as the mother of several ugly, blind children and kicks Hans out of the car to prevent that future from happening. Lisa then suggests to Selma that she go through artificial insemination.
When the day comes for Homer to take Bart and Lisa to Duff Gardens, he falls ill from food poisoning after eating a hoagie that became spoiled days after he took it home from a company picnic. In an attempt to give Selma a taste of motherhood, Marge nominates her to take the kids to Duff Gardens while she stays home to look after Homer.
When the trio arrives at Duff Gardens, Bart and Lisa wear Selma out, especially when they go on the Little Land of Duff ride and Bart dares Lisa to drink the toxic "water". Lisa is confused, but Bart mocks her until Selma intervenes, shouting at Bart to shut up and ordering Lisa to drink the water. When Lisa takes a sip, she hallucinates, grows violent and paranoid, and wanders away from the ride, tripping out to the parade music. While Selma is looking for Lisa, Bart gets on a roller coaster called The Barrel Roll and ends up having to be rescued after the car stops in the center of one of the inversions. Lisa is soon found swimming nude in the Fermentarium, returned to Selma and given pills by an unlicensed doctor.
After Bart and Lisa return home, Selma decides she can live without children and adopts Jub-Jub, Gladys' pet iguana.