The Willards from Terre Haute, Indiana travels abroad for the once-in-a-lifetime vacation in Paris, France. Harry Willard believes that the greatest problem will be avoiding tap water, but bringing his three children will prove to be more troublesome.

Harry Willard, a Terre Haute plumbing contractor, and Katie, his wife, have spent years planning and saving for a trip abroad. Finally their dream is realized, and along with their three children--teenagers Amy and Elliott, and 12-year-old Skipper--they arrive in New York to board the Europe-bound S.S. United States. Even before the ship has left the pier, Harry's troubles begin when Amy becomes involved with playboy Nick O'Mara, the son of a giddy American who has married into European royalty. Once in Paris, Katie acquires a chic coiffure which captures the eye of Rudolph, a handsome Hungarian, and Elliott falls for an intriguing French girl. Harry, on the other hand, tries to please little Skipper by taking him on a tour of the Paris sewer system, and the two become hopelessly lost in the underground labyrinth. The family then moves on to the Riviera where Harry manages to straighten out everyone's romantic problems, but not before he knocks Rudolph unconscious at a cocktail party given by Nick's countess mother. Their vacation over, the Willards return to the comparative peace and quiet of their Terre Haute home.