I'd watched this one last week and didn't get around to writing anything down about it. There's not much to say, really -- it's a pretty routine wartime espionage thriller about double-agents operating in London, set during WWI but designed as a bit of propaganda for 1940 audiences.
The plot itself is a bit confusing, packing so many character twists into its hour running time that the motivations and relationships aren't always clear.
The highlight is Boris Karloff in the role of a double-agent. He's always fascinating to watch and gives the part his all.