This is the fourth in a series of movies that began with National Lampoon's Vacation in 1983 and feature the family headed by Clark Griswold (Chevy Chase) going on wacky vacations. This time, the Griswolds visit Las Vegas. Clark immediately goes to the blackjack table and starts blowing all his money, continually encouraged to spend more and more by a taunting dealer, Marty (Wallace Shawn). Ellen Griswold (Beverly D'Angelo) becomes smitten with the lounge singer Wayne Newton (playing himself), who invites her to sing onstage with him. Their son Rusty (Ethan Embry) is incredibly lucky playing dice, and he is virtually adopted by a family of gangsters who see him as their meal ticket. Daughter Audrey (Marisol Nichols) gets hooked up with her wild cousin Vickie (Shae D'Lyn), who takes her to sleazy dance clubs. White-trash cousin Eddie (Randy Quaid), who lives on a former A-bomb test site in the nearby desert, also gets involved with the capers.