Lisbon Story [1946] [DVD]

The basic plot concerns the efforts of British intelligence to rescue from France an atomic scientist. They give David Farrar the identity of a French agent and send him back to France to contact the Nazi authorities so that he can worm his way into their good books and effect the escape of the scientist, aided by his girlfriend, who is French and pretending to be a collaborator.

Note, there are a couple of slight sound dropouts at the start of the film where the volume level seems oddly high during the theatre scenes.