“Yes. The obvious always appears simple.”
Dr. Franz Tobel (William Post Jr.) is a scientist who has invented a revolutionary bomb guidance system. Sherlock Holmes (Basil Rathbone) helps to get him out of Switzerland before he can be taken by the Gestapo. Holmes places him under the supposed watchful eye of Dr. Watson (Nigel Bruce). Tobel sneaks away and visits his fiancée Charlotte Eberli (Kaaren Verne). He gives her an envelope containing a coded message to give to Holmes should anything happen to him. The German’s try to abduct him, but the attempt fails.
The next day Tobel successfully demonstrates the bombsight for Sir Reginald Bailey (Holmes Herbert) and observers from Bomber Command. Tobel is willing to offer the use of the system but insists that he retain the secret of it. He insists on supervising the construction of it. To guard against theft his invention is separated into four parts. Each part is given to four separate Swiss scientists known only to him. 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. Instead of the coded message, the message inside is from Holmes’ nemesis, Professor Moriarty (Lionel Atwill).
Holmes disguises himself as one of Moriarty’s henchmen and searches the Soho district for clues. He is captured by Moriarty, but then rescued by Watson. Holmes returns to Charlotte's flat to search for clues. He finds impressions of the message left on a notepad. By immersing the pad in fluorescent salts and photographing it using ultraviolet light he is able to read the impressions. The impressions are in code. The message is a variation of an alphabet substitution code made up of a series of stick figures. Holmes breaks the code on the first three lines. It shows the identities and locations of three of the scientists. The fourth line, however, is a modified version of the code that is elusive to him. Holmes finds out that Moriarty has murdered the first three scientists and stolen their parts. Meanwhile, Moriarty, also unable to break the fourth line, tortures Tobel for the name of the fourth scientist. Moriarty’s intent is to sell the devise to the highest bidder. Holmes deduces the change in the code and breaks the fourth line. But Moriarty is not far behind him.
“Sherlock Holmes and the Secret Weapon” was released in 1943 and was directed by Roy William Neill. This is the first movie of the series to be directed by Roy William Neill. He will continue to direct the remaining Universal movies. In total he will direct 11 of the 14 in the series. It is credited as being based on Doyle’s novel “The Adventure of the Dancing Men”, written in 1903, however, the only thing that was taken from the original story was the code. It is the 4th in the Rathbone/Bruce series of Sherlock Holmes movies. It was also the first of four of them that lapsed into the public domain. There is also a colorized version of the film. It is also the first of the series that features the Inspector Lestrade character, played by Dennis Hoey and the second of the series to feature Professor Moriarty, and the second time he dies.
Professor James Moriarty only directly appears in two of the Sherlock Holmes stories, “The Final Problem” and “The Valley of Fear”. He’s mentioned in five other stories, “The Empty House”, “The Norwood Builder”, “The Missing Three-Quarter”, “The Illustrious Client”, and “His Last Bow”. According to Sherlock Holmes in “The Final Problem” Moriarty is rather like a Victorian mafia leader.