When a Nazi saboteur jeeringly predicts to the nation new depredations via the radio 'Voice of Terror', the Homeland Security Inner Council summons Sherlock Holmes (Basil Rathbone) to help in the crisis. Holmes and his companion, Dr. Watson (Nigel Bruce), receive a visitor on the first night of their investigation; a man falls dying from a knife in the back on their doorstep. His last word leads Holmes into the slums where he encounters Kitty (Evelyn Ankers), the sweetheart of the slain man, who promises to help the investigation in any way she can.