i'll go with this:-
one of the earliest espionage movies, this is a monchromatic silent German film.... utterly engrossing from start to finish, and is probably Lang's best piece of work
everything is just so perfect with this, the early noir ambience, the framing
additional info here:-
Spione - Wikipedia, the free encyclopedia
the entire movie's on youtube if you so desire to watch it, here's the trailer from the restored version:-