Sherlock Holmes and the Secret Weapon (1943) is the fourth in the Basil Rathbone/Nigel Bruce series of Sherlock Holmes films.
Holmes successfully removes Professor Tobel and his new invention - the "Tobel Bombsight" (analogous to the real-life Norden Bombsight) - from Switzerland to safety in England under the noses of German agents. However once in England, Tobel disappears, kidnapped by Holmes' arch-nemesis, Professor Moriarty, now in league with the Nazis. However Tobel has left a cryptic message in code behind (taken from the Arthur Conan Doyle story The Adventure of the Dancing Men).
Holmes cracks the code and tracks Tobel down, in the process utilizing his skill in disguises, appearing as a Swiss inventor, a criminal Lascar, and an elderly German bookseller.