Sherlock Holmes And The Secret Weapon 1942

Sherlock Holmes and the Secret Weapon (1942) is the fourth in the Basil Rathbone/Nigel Bruce series of 14 Sherlock Holmes films which updated the characters created by Sir Arthur Conan Doyle to the then present day. The film is credited as an adaptation of Conan Doyle's 1903 short story "The Adventure of the Dancing Men," though the only element from the source material is the dancing men code. Rather, it is a spy film taking place on the background of the then ongoing Second World War with an original premise. The film concerns the kidnapping of a Swiss scientist by their nemesis Professor Moriarty, to steal a new bomb sight and sell it to Nazi Germany. Sherlock Holmes and Dr. John Watson have to crack a secret code in order to save the country.
Sherlock Holmes (Basil Rathbone) pretends to be a Nazi spy to aid scientist Dr. Franz Tobel (William Post Jr.) and his new invention, a bombsight, in escaping a Gestapo trap in Switzerland. Holmes and Franz fly to London, where Holmes places him under the protection of his friend, Dr. Watson (Nigel Bruce). The scientist slips away against Holmes' instructions for a secret reunion with his fiancee, Charlotte Eberli (Kaaren Verne), and gives her an envelope containing a coded message. He tells Charlotte to give it to Holmes if anything should happen to him. German spies' attempt to abduct Tobel as he leaves Charlotte's apartment is foiled by a passing London bobby.
Tobel successfully demonstrates the bombsight for Sir Reginald Bailey (Holmes Herbert) and observers from Bomber Command. Tobel, now under the protection of Inspector Lestrade (Dennis Hoey) and Scotland Yard, tells Sir Reginald that, although willing to provide the British with his bombsight, only he will know its secret and has a complex plan for its manufacture to keep the secret safe. He separates his invention into four parts and gives one to each of four Swiss scientists, known only to him and not to each other, to construct separately. Soon after, Holmes receives a call from Lestrade telling him that Tobel has disappeared. Holmes goes to Charlotte's flat, where he receives Tobel's envelope. Rather than the coded message, the message inside is from Holmes' nemesis, master criminal Professor Moriarty (Lionel Atwill), who is now working for the Germans.
Disguising himself as Ram Singh, one of Moriarty's old henchmen, Holmes searches the Soho district for information. He encounters two henchmen Peg Leg (Harold De Becker) and Jack Brady (Harry Cording), but is captured by Moriarty. Holmes is put into the false bottom of a sea chest, but is rescued when Watson and Lestrade observe the henchmen struggling with its unusual weight. Holmes returns to Charlotte's flat to search for clues to the message's contents. He finds impressions of the message left on a notepad page by immersing it in "fluorescent salts... and then photograph(ing) it by ultraviolet light." Holmes breaks the first three lines of a cunningly modified substitution cipher etc..