After stuffing themselves with turkey on Thanksgiving, it is time to take the annual Christmas card family photo, and when Bart and Lisa complain about it, Marge notes that they will grow to appreciate the photos when they become older and have children of their own. Lisa questions why Marge would assume they will even have children in the first place, and the episode jumps thirty years into the future via a series of Simpsons Christmas cards. The photos finally settle on a future where Bart is a deadbeat, divorced dad with two sons whom he does not see often; Lisa is a successful businesswoman who is married to Milhouse and has a rebellious daughter named Zia; and Maggie is the lead singer of a famous band and in the late stages of pregnancy. In his apartment at the former Springfield Elementary, Bart is visited by his sons, who inform him that their mother Jenda teleported them to his place because she wants him to act like a proper father by having him spend time with them. However, he plans on dropping them off at his parents' house instead. Meanwhile, Lisa fears that Zia is spending too much of her time going into the "Ultranet", a digital world that people enter with their consciousness by plugging themselves into a laptop. Milhouse suggests to Lisa that she spend time with Zia in order for them to have a better connection, so Lisa decides to take Zia to her parents' house. Meanwhile, Maggie flies home from London to Springfield to celebrate Christmas with her parents.
When Bart and Lisa arrive at their parents' home, they stay there with their children. Unfortunately for Lisa, she only gets unhelpful advice from Marge on how to be a better parent and Zia continues to go into the Ultranet. Meanwhile, Bart is heartbroken to find out that Jenda has remarried while he has not found anyone new. Feeling depressed, he tells Homer to take his grandsons out. The boys become angry with their father for not spending time with them, but the two have a great time with their grandfather. Bart and Lisa then encounter each other in their old treehouse, where they become slightly drunk and talk about how difficult parenting is. After exchanging inspirational advice, they realize that they need to try harder to connect with their children. Meanwhile, upon arriving in Springfield, Maggie starts experiencing contractions and Kearney, now a taxi driver, drives her to the hospital.
Homer takes Bart's sons to a cryonics facility where Grampa has been frozen alive to prevent a disease from killing him. Although a cure has now been discovered, he is kept frozen by Homer because it is cheaper than paying for a nursing home and because Grampa has constantly been rude to him. Homer says to the boys that they should give their father another chance, since he knows Bart loves them. At that point, Bart arrives and apologizes to his sons, admitting how much he treasures them. Touched, the two boys forgive him for not having included them in his life much, while an inspired Homer decides to unfreeze Grampa and forgive him as well. Meanwhile, Lisa goes into the Ultranet to find Zia and discovers a door leading into Zia's private world. Entering it, Lisa is overjoyed to find that Zia has hung a poster of her next to a series of posters depicting historical women who have made a difference in the world. When Zia arrives, Lisa thanks her for looking up to her and the two reconcile at last, and secretly hides her life as a party poser. With the conflicts resolved, Bart and Lisa gather their children in preparation for a new Christmas family photo. Marge arrives with Maggie, who has given birth to a baby girl. The Simpsons gather into a group just as the family pets (who have evolved greatly over the past thirty years) take the new photo.