Type in the Shadows
The first anti-Nazi film produced by a major studio, Confessions of a Nazi Spy (1939) directed by Anatole Litvak, follows Edward G. Robinson in the role of FBI agent Ed Renard (the fox?) as he investigates a Nazi espionage ring headed up by dedicated National Socialist, Dr. Kassell, played by Paul Lukas in a part that suggests Fritz Kuhn, the self-styled fuhrer of the German American Bund.
From the first clues in Scotland that the Nazis have infiltrated the US, to the suspenseful pursuit of Dr. Kassell and others, we are witness to spy rings, violence, deceit, and a new and egregious evil come to our shores. The film hit the viewing public with a wallop; it was an expose the times.
It is also one of my favorite 30s era movie types.