Sherlock Holmes (Basil Rathbone) pretends to be a Nazi spy to aid scientist Dr. Franz Tobel (William Post, Jr.) and his invention (a bombsight), while in Switzerland. Holmes and Franz fly back to London, but Franz slips away for a secret meeting with his fiancée, handing her a coded message to be presented to Holmes should anything happen to him. Holmes receives a call telling him that Tobel has disappeared. Holmes goes to Charlotte's apartment, where he receives Tobel's envelope. Rather than the coded message, the message inside is from Holme's nemesis, master criminal Professor Moriarty (Lionel Atwill). Moriarty has abducted Tobel to retrieve the secrets to his invention, which Tobel had given in four sections to trusted associates. Holmes returns to Charlotte's apartment to search for the four missing parts to the encoded message. Holmes is able to deduce three of the message's parts, but cannot figure out the fourth. Meanwhile, Moriarty is torturing Tobel in order to uncover the four parts to the message. Who deciphers the encoded message first - Holmes or Moriarty? Lots of action and thrills to come, making this one of the best Holme's classics ever made! (65 minutes - 1943 - Black & White - 4:3).