Diplomatic Courier (1952) on Netflix

Plot summary

Mike Kells, a diplomatic courier for the State Department, comes back to Paris from a mission and is reassigned to Salzburg, where his Navy friend Sam Carew is to hand him a top-secret document on a railway station platform. Joan Ross is on the flight with him. At the station two men tail Carew, who is forced to ignore Kells; Kells boards the same train and sits near a woman Carew seems to know. Col. Mark Cagle and Sgt. Ernie Guelvada of the Army question him, believe the woman has a part in it, and send him to Trieste with Guelvada to find her. She is Janine Betki, a singer who may be a Soviet agent. Kells visits the club where she once performed and sees Joan there too.