Professor Moriarty (George Zucco) has at long last been brought to trial for murder. But the ‘Napoleon of Crime’ is acquitted after the court finds a lack of sufficient evidence. Moments after the judge releases the defendant, Sherlock Holmes dashes into the courtroom with proof that will destroy Moriarty’s alibi and send the professor to the gallows. Alas, he is too late and the criminal mastermind is set free.

Moriarty wastes no time in plotting his next crime, but in order to be successful he must divert the attention of the Great Detective. Enter Miss Ann Brandon (Ida Lupino), who calls on Holmes and his companion Dr. Watson (Nigel Bruce) after she and her brother receive anonymous letters containing a drawing of a man with an albatross hung around his neck, and a date written above the picture. Their father received the same baffling letter years before and was found murdered on the date inscribed in his letter.

Are these mysterious letters but erroneous distractions? Are they clues to a case irrelevant to the exploits of the evil Professor Moriarty? Or are these portents of disaster inexorably linked to the master criminal’s plan to commit a crime that will shake the very foundation of the British Empire? It is for Holmes and Watson to sort out this mystery and, hopefully, eliminate the menace of Professor Moriarty.