The secret of the Lady of Secrets (Ruth Chatterton) is that her so-called younger sister, Joan (Marian Marsh), isn't her sister at all but is actually her daughter. Her lover, Michael Whittaker (Lloyd Nolan), was killed in the war and his domineering father (Lionel Atwill) insisted that the child she was carrying, out of wedlock, be reared as her younger sister and not as a bastard child.. When the truth finally emerges, Mr. Whitaker has Celia committed---but she escapes in time to keep her daughter, Joan (Marian Marsh), from marrying a man, David (Otto Kruger), she does not love.