Spoiler alert: i know this is obvious but I think the primary theme of the film is Duplicity. Everyone is screwing over everyone else. Diello is screwing his employers (i.e. The British government and their war effort), the Germans screwing Diello (paying him in counterfeit pounds), the Countess screwing over Diello by stealing the money but, in fact, screwing herself, too. Also, the Germans were screwing each other with Col. Von Richter usurping Von Papen from the spy operation. Even the innocent cleaning lady inadvertently screws over Diello by being...conscientious.