A fabulously expensive diamond is to be taken from London to Edinburgh by train, and Sherlock Holmes is engaged to guard it. Part of Universal's Sherlock Holmes film series set in 1940s Britain.

"Sherlock Holmes: Terror By Night" (1946) Starring Basil Rathbone, Nigel Bruce Based on the stories by Sir Arthur Conan Doyle Written by Frank Gruber Produced & Directed by Roy William Neill

More info: en.wikipedia.org/wiki/Terror_by_Night