The song originally appeared in Alfred Hitchcock film "The Man Who Knew Too Much", where it appears diegetically and serves an important role in the film's plot. In the film, Day plays a retired popular singer, Jo McKenna, who, along with her husband (played by Jimmy Stewart) and son, becomes embroiled in a plot to assassinate a foreign prime minister. After foiling the assassination attempt, Jo and her husband are invited by the prime minister to the embassy, where they believe their young son is being held by the conspirators. Jo sits at a piano and plays "Que Sera, Sera", singing loudly in the hope of reaching her son. Upon hearing his mother play the familiar song, Jo's son whistles along, allowing Jo's husband to find and rescue the boy, just before he was to be murdered by the conspirators to the assassination attempt.