Jack Lemmon stars as crabby American World War II veteran Bob Traven, who travels to Italy on a business trip and reunites with wartime buddy Antonio (Marcello Mastroianni), whose freewheeling Neapolitan lifestyle goes against all of Traven's uptight sensibilities. On his three-day stay in Naples, Traven learns from Antonio's unwavering enthusiasm and discovers that his former flame, Antonio's sister, still holds a place for him in her heart.