Clark Griswold, wanting to spend more time with his wife Ellen and children Rusty and Audrey, decides to lead the family on a cross-country expedition from the Chicago suburbs to the southern California amusement park Walley World, billed as "America's Favorite Family Fun Park." Ellen wants to fly, but Clark insists on driving, so he can bond with his family. He has ordered a new car in preparation for the trip, but the dealer claims that it will not be ready for six weeks. Clark is forced to accept a Wagon Queen Family Truckster, an ugly, out-sized station wagon, as the car he brought to trade in has already been hauled away and car crusher.
The Griswolds win a vacation tour across Europe where the usual havoc ensues.
With Christmas only a few weeks away, Chicago resident Clark Griswold decides it is time to get a Christmas tree. He gathers his wife Ellen, daughter Audrey, and son Rusty and drives out to the country where he picks out a huge tree. Realizing too late that they didn't bring any tools to cut the tree down, they are forced to uproot it instead, before driving home with the tree strapped to the roof of their car.
Clark Griswold has invented a long-life food preservative, earning him a large bonus check. He announces to his family that he is taking them on vacation. Part of the reason for the trip is for Clark and Ellen to renew their wedding vows. Excitement wanes, however, when Clark says they are headed to Las Vegas. His wife, Ellen, and teenage daughter, Audrey, have their doubts, as Las Vegas is not known for its family-friendly atmosphere, while teenage son Rusty appears to be more enthusiastic.
The story begins with Cousin Eddie at his latest workplace, a nuclear facility where he 'works' alongside a monkey. When the monkey outperforms him in every test (specifically mental agility), the decision is made to fire him. Upon finding out the news, the two get into an argument which results in the monkey biting him.
Hoping to bring his family closer together and to recreate his childhood vacation for his own kids, a grown up Rusty Griswold takes his wife and their two sons on a cross-country road trip to the coolest theme park in America, Walley World. Needless to say, things don't go quite as planned.
