Over the course of the vacation, Rusty's marriage is saved and his family grows closer together even after getting stuck upside down on a roller coaster at Wally World for several hours.
This sequel follows Rusty Griswold (Ed Helms), who is now an adult working for an economy airline. Though well-meaning, he embarrasses his children James (Skyler Gisondo) and Kevin (Steele Stebbins), is mild-mannered with his wife Debbie (Christina Applegate), and is bullied at work (cameo by Ron Livingston). Though far bigger and the older brother, James is constantly bullied by Kevin. After a dinner with their friends (cameo by Keegan-Michael Key), Rusty decides his family needs a vacation to reconnect and decides to recreate the childhood trip with his parents to the amusement park Wally World (See: National Lampoon's Vacation).
Rusty rents a foreign car that has two gas-tanks (and an unexplained plug), a remote with unexplained buttons and a GPS that speaks in an angry Asian dialect. As they drive, Rusty attempts unsuccessfully to get his family to sing Seal's "Kiss from a Rose." At a motel, James meets a pretty girl who is scared away when Rusty tries to wing-man for him but comes off as a child predator. He also unsuccessfully tries to have sex in the motel shower with Debbie, giving up after they find dried blood and a ball of pubes in the bathtub. The family stops at Debbie's college where Rusty discovers his wife has a far more expansive sexual history than she let on. Meanwhile, Debbie tries (unsuccessfully) to complete a beer event being thrown by her sorority, instead puking everywhere. They are also chased down the highway by a large truck (wherein they find one button on the remote works to eject the car's fender, another button causes the driver's seat to rotate). Things come to a head when a local redneck convinces them a sewage pond is a natural hot springs and robs their car while they are literally swimming in shit.
With no recourse, the family visits Rusty's sister Audrey (Leslie Mann). Audrey's husband Stone (Chris Hemsworth) is incredibly successful, wealthy, physically impressive and has just begun ranching cattle. He encourages Kevin to beat up James and flirts with a clearly flattered Debbie. Though Debbie's marriage seem picturesque, it is clear turmoil bubbles under the surface. Rusty's family leaves after Rusty, while trying to prove himself manly, accidentally runs over and kills one of Stone's prize cows.
The Griswolds then experience many other mishaps. Their whitewater rafting guide (Charlie Cox) becomes suicidal when his fiancee breaks up with him just before their trip, causing the Griswolds to abandon ship just before the guide goes over a waterfall. At the Four Corners, Rusty and Debbie go to have sex on the monument, only to discover it is the site of a sex ring that they then get caught up in when police arrive. One positive is that James is encouraged by the girl he met earlier in the film to stand up to his brother, causing Kevin to finally respect him. It all reaches a head when the car breaks down and eventually explodes (due to one of the remote buttons) in the middle of the desert. They are then saved by the truck driver (cameo by Norman Reedus) from earlier, who had only been following them because he found Debbie's wedding ring, which had fallen off at a truck stop.
The driver drops them off at Rusty's parents house, where they plan to fly back home. Clark (Chevy Chase) and Ellen (Beverly D'Angelo) welcome them warmly. While there, Rusty discovers Debbie was secretly reading a book about broken marriages. Rusty confronts her and the two eventually patch things up. Clark convinces Rusty to finish the trip to Wally World. He also lends Rusty the old station wagon from the original film.
Once there, the Griswolds wait in line all day for one roller coaster. As they are about to board the last run of the day, they are cut off by Ron Livingston's character and family, who have bought fast passes. The families fight each other with the Griswolds emerging victorious and claiming the seats on the roller coaster. On the ride, the whole family begins to sing "Kiss from a Rose" when the ride stops. They are stranded upside down for several hours, but it is clear they have all bonded over the course of the vacation.
The film ends with Rusty sending the children back home on their own so he can take Debbie to Paris. Of course, being the Griswolds, Rusty and Debbie's seats are situated in between the airplane bathrooms, where they will be stuck for the entirety of the flight.
The film also has cameos from Nick Kroll, Tim Heidecker, Kaitlin Olson, Michael Peña, Colin Hanks, John Francis Daley and Seal.
Thanks Evan B!