When a gentlewoman is found dead with her throat torn out, the villagers blame a supernatural monster. But Sherlock Holmes, who gets drawn into the case from nearby Quebec, suspects a human murderer.

Sherlock Holmes saves noted Swiss physicist Franz Tobel from the Gestapo in Zurich and smuggles him to London. There, Tobel is reunited with his wife, Charlotte, to whom he gives a coded message in the event he disappears. Tobel presents the weapon he developed to government officials, and when he is subsequently abducted by arch-villain Professor Moriarty, Holmes and Dr. Watson risk their lives to find him.

Holmes and Watson travel to Washington D.C. in order to prevent a secret document from falling into enemy hands.

During WWII several murders occur at a convalescent home where Dr. Watson has volunteered his services. He summons Holmes for help and the master detective proceeds to solve the crime from a long list of suspects including the owners of the home, the staff and the patients recovering there.

When a Nazi saboteur jeeringly predicts to the nation new depredations, via their radio 'Voice of Terror', the Intellegence Inner Council summons Sherlock Holmes to help in the crisis.