Wealthy American businessman Robert Talbot (Rock Hudson) owns a villa on the Ligurian coast, where he and his Roman mistress Lisa Fellini (Gina Lollobrigida) spend September of each year. When Robert moves up his annual visit to July and calls her en route from Milano, she cancels her wedding to Englishman Spencer (Ronald Howard (British actor)) and rushes to meet him. Upon his arrival at the villa, Robert discovers that, in his absence, his major domo, Maurice Clavell (Walter Slezak), has turned the villa into a hotel, currently hosting a group of teenage girls, including Sandy (Sandra Dee), and their chaperone, Margaret Allison (Brenda De Banzie). Their departure is delayed when Margaret slips on the cork of a champagne bottle opened by Robert and is forced to spend a day in the hospital. Four teenage boys who irritated Robert on the drive to his villa, including Tony (Bobby Darin), set up camp right outside of the villa and begin courting the girls.