Sherlock Holmes (Basil Rathbone) and his partner Dr. Watson (Nigel Bruce) are attempting to help Scotland Yard in solving a series of strange, seemingly random murders. The gory common denominator is that each young female victim has had her right forefinger severed. The investigation subsequently leads to an organization of hypnotists and a beautiful but enigmatic woman. The diabolical Professor Moriarty, despite premature reports of his execution in Montevideo, is thought to be implicated. Holmes and Moriarty face off in the climactic scene, when, briefly, it appears that our hero's nemesis may win the day.