The mystery in this one is as old as dirt. It goes further back than the Erroll Flynn movie, Footsteps in the Fog. It shows up also in Madame Sara, a story first published in 1902. The author of the teleplay for this, Steve Boccho, could have read it as it was published in the popular anthology, The Rivals of Sherlock Holmes, in 1971. A British one season TV series followed, but I can't recall if this particular story appeared in it.
Review of Affair of the Heart
