This is the third of seven collaborations between Josef von Sternberg and Marlene Dietrich made between 1930-35. The last six were for Paramount and are exotic studio melodramas set in romantic places. Critics search for unifying themes, but what they uniquely share is the director's visual style, and the fascination of his camera for his star.
Dietrich plays a sex worker who turns spy for Austria in WWI. Her mission is to take down her Russian counterpart (Victor McLaglen) which she does, but of course they fall in love and she saves him and is shot for treason... But really this is a film about how von Sternberg lights his great leading lady. Plus a lot of fatalism and atmosphere with cigarettes and snowstorms.
And Marlene is dressed magnificently. In my view, this is the least of their films. Mostly because McLaglen is disastrously cast and a limited actor anyway. Dietrich gives a languid, opiated performance which is probably intended to be mysterious, but just slows everything down. The narrative of romantic espionage is commonplace. The dialogue is absurd.
But in a way, none of this matters. This is an artistic production of extraordinary glamour, and that's why these films survive. No one can make pictures like this now; they're rare blooms which are rooted in their period and its technology. And in the unique relationship between the director and his star and Paramount's willingness to indulge them.