A friend of Dr. Watson's wife comes to Watson's house, frantic because her husband, Isa Whitney, an opium addict, has gone missing. Watson helps her pull him out of the opium den and sends him home. Watson is surprised to find that Sherlock Holmes is there too, in disguise and trying to get information to solve a different case about a man who has disappeared. Watson stays to listen to Holmes tell the story of the case of Neville St. Clair.