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The Unguarded Hour opens with prosecutor Sir Alan Deardon (Franchot Tone) in the midst of a murder trial. He gets his conviction, while his wife, Lady Helen (Loretta Young), sits furrow-browed on the sidelines. Helen had witnessed the murder and thus can prove that the condemned man (Dudley Digges) is innocent. But she cannot come forth with this information without revealing a past indiscretion in her husband's life, for which she is being blackmailed. To make a long story short, which MGM didn't, Sir Alan ends the film not as a prosecutor in a murder case, but as the prosecuted. Based on a play by Ladislas Fodor and Bernard Merivale, The Unguarded Hour represented the Hollywood debut of that splendidly satanic villain Henry Daniell, cast to type as the blackmailer.