The secret weapon is a new bombsight which could hasten the outcome of World War II, and both the Allies and the Nazis are in a desperate race to secure it for themselves. Super sleuth Sherlock Holmes (Basil Rathbone) and his trusty assistant Dr. Watson (Nigel Bruce) are assigned to find the kidnapped scientist who developed the secret weapon, only to be foiled by Holmes' nemesis, the evil Professor Moriarty (Lionel Atwill). Based on the Sir Arthur Conan Doyle story THE ADVENTURE OF THE DANCING MEN, this Holmes case transplants the Victorian sleuth into the realm of WWII espionage and is also the first of the films to introduce Dennis Hoey as Scotland Yard detective Inspector Lestrade.