Just wanted to second the other user's comment.
I saw this last night as part of a Michael Powell/Emeric Pressberger retrospective underway at the American Cinemetheque. There are some unlikely aspects to the plot, but on the whole this is well crafted WWI thriller with a remarkable level of moral complexity, especially given that it was made and released just as England was entering a second war against Germany.
The protagonist (hero?) (played by the extraordinary Conrad Veidt) is a German officer on a spy mission and he is, in many respects, a quite admirable character. For the first half of the film, it's almost entirely from his point of view. It's hard to imagine Hollywood filmmakers EVER having the confidence that Powell and Pressberger clearly had in the intelligence of their audience, allowing them to actually like and admire an enemy agent.
While "The Spy in Black" eventually does come down squarely on the side of the English, the agents of the Kaiser come off only as perhaps a hair more ruthless than those fighting for king and country.
Of course, the Germany that England would be fighting within a few a few months would be far, far worse. This film is a potent reminder that while World War II might have a morally clear "good" war because of the vast evil of the Nazis, World War I was a horse of a far grayer color.
With sophisticated, occasionally black humor, this is a neat bit of old-fashioned movie entertainment with some genuinely intriguing differences. Enthusaistically recommended.
