Pazuzu, Farnsworth's gargoyle breaks out of the Planet Express building. Professor Farnsworth shouts at him, saying, "Pazuzu you ungrateful gargoyle. I put you through college and this is how you repay me!" before gargoyle droppings hits his face. He heads to the ship, forcing Fry and Leela to strap themselves completely to their seats and Bender bolts himself to the wall. The Professor flies out into space but is slowing down traffic, everyone scolding at him. Farnsworth inadvertently has the high beams on, incinerating a direction sign and blowing up Deep Space 9 while searching for Pazuzu.
Forgetting about Pazuzu, Farnsworth redirects to Florida for a nice lunch. Unfortunately, his lifetime discount is expired and he activates his nuclear-powered teeth, which runs amok after tasting human blood. Fed up with his senility, the Planet Express crew take him to a day spa, where he is properly massaged. Because he is 161 years old, he is put in the anti-aging pits. But Bender pumps the pits too hard and the Professor is tossed up and down until the tar sinks into the ground. The ground gives way beneath the crew and they all fall in. Everyone climbs out and gets cleaned up; the Professor is looking middle aged, but the others are teenagers.
While Farnsworth tries to fix things, the others try to settle into their teenage lives. Amy goes home to Mars where her mom is angry cause she wants a grandchild, and her dad makes fun of her fat physique; Hermes goes home with LaBarbara and Dwight; Leela tries to enjoy a normal teenage life in the sewers while Bender, Fry and Zoidberg stay at Planet Express. Fry (who has a cracked voice) soon begins dating Leela but in a sewer race with Mandy and Moose, they destroy a Martin Luther Thing, Jr.High School.
Soon, the Professor discovers time-altering chronitons on their DNA and Bender's RNA and finds a way to get them back to their normal ages; Leela declines, and continues her teenage life. The others get into the Bacterial Spew Chamber which "coughs" a gas on them. Unfortunately, the machine has the opposite effect - they are getting younger by the minute. Farnsworth tries to think of another solution but the kids' constant whining leads him to hire Leela as the babysitter. She discovers the existence of the Fountain of Aging from a story book and contacts the Professor. He picks up the kids while Leela stays grounded, willingly, until she sneaks out at night. She guides the now-much-younger Farnsworth to the fountain, which is on top of a burnt-out sun. As time is running out, they locate it.
Norman, one of Zoidberg's siblings, jumps in, growing older until he dies and crumbles. Worse, the others have become fetuses and Bender is a blueprint disc. Farnsworth quickly gets them in but the current carries them off as they age. To save them, Leela jumps in to save them and gives up her teenage appearance. They emerge in their underwear but the Professor is still stuck. Just then, Pazuzu rescues him. Scans indicate that Farnsworth is even older and Leela and Amy feel a bit younger. The Professor then repays the gargoyle by freeing him. The final scene shows Pazuzu has moved to Paris, had a son and that he has been telling him the events of the episode.