A malfunctioning time machine at a ski resort takes a man back to 1986 with his two friends and nephew, where they must relive a fateful night and not change anything to make sure the nephew is born.

Rusty Griswold takes his own family on a road trip to Walley World in order to spice things up with his wife and reconnect with his sons.

Five years after the events of the first film, Lou Dorchen and Nick Webber have become Wealth and Celebrity, with Lou becoming a multi-billionaire and Nick being a successful music singer. At Lou's celebratory party, Lou is shot in the groin. Jacob (Lou's son) and Nick drag him to the hot tub time machine and activate it to travel back in time to find and stop the killer. When they awaken they find themselves ten years in the future, where Jacob is in charge of Lou's mansion. After determining that they are in an alternate timeline where Lou's killer is from this future, they go to their friend Adam Yates's home, only to meet his son Adam Yates Stedmeyer (Adam Jr.) who is engaged to a girl named Jill.