I watched Sherlock Homes and the Secret Weapon because that series of films starring Basil Rathbone as Holmes were a bit of a mystery to me. They certainly banged them out: 14 were made between 1939 and 1946, and updated to the present, often with the lightest of nods to the Conan Doyle canon.
Rathbone plays Holmes, Nigel Bruce plays Watson, Moriarty appears, and is killed off a couple of times. But, as in the original, of course, Moriarty never dies.
In 1942, in Secret Weapon, Holmes has to spring a scientist from Switzerland under the eyes of watching Gestapo agents, and once in London spring him once again from the clutches of Moriarty. Of course, it is a propaganda film. The MacGuffin is a bombsight that the scientist has designed that is far more accurate (yes, I heard it as “bombsite” in the film until I saw it assembled).
The Conan Doyle reference is to the Dancing Men code, used by the scientists for a critical plot point. Watson is bluff. Lestrade is a comic plodder.
The moment is certainly a spoiler: yes, Holmes foils the plot and saves the scientist and the RAF gets its bombsights. This is from the very end of the film, when Holmes and Watson are watching squadrons of bombers equipped with the sights heading for Germany. (The usefulness of that is for another post on another day). Shakespeare is invoked. But unlike Nolan’s Dunkirk, when audiences first saw this film, in 1942, they didn’t know how things were going to turn out. The TV version I saw had left an advertisement for war bonds on the print they screened, after the credits.