American lawyer Michael Hamilton (Gable) of Philadelphia, Pennsylvania travels to Naples, Italy to handle affairs relating to his late brother, Joseph's estate. In two days, Hamilton is to be wed in the US to his fiancee, Linda. Once in Naples, he discovers that his brother had a son. Nine year old, Nando who is being cared for by Lucia, a sexy sister-(not)-in-law (Loren). The late Joseph Hamilton and Lucia's sister drown in a boat accident. Joseph Hamilton's wife who he left in 1950 is alive in Philadelphia. Michael Hamilton who in the opening narration states, "he was here before with the 5th US Army" in World War II. Hamilton wants to settle his deceased brother's estate with Italian lawyer Vitalli (De Sica). To his dismay, Hamilton finds his brother spent a fortune in fireworks. Lucia works as a cabaret singer. After seeing Nando handing out racy photos of Lucia at 2 A.M.; Michael wants to enroll Nando in the American School at Rome. Lucia wins custody of Nando. Despite the age difference, romance soon blossoms between Michael and Lucia. Mike decides to stay in Italy.
This was the last film to be released within Gable's lifetime (his final film, The Misfits, was released posthumously) and his last film in color. One of the highlights of the film is a tongue-in-cheek musical number by Loren called You Want to be Americano.