This is a very absorbing, love-interest notwithstanding, film that covers the months before the invasion of Poland at the beginning of WW II. Diplomatists and spies are trying to anticipate what move Germany is going to make to initiate a second European war and trying to decide what information they are receiving is reliable or convincing. There is a continuous thread of tension with minimal overtly violent scenes. It is also visually scenic in that there are a variety of locations and sunny settings despite the main setting being the streets of Warsaw. I wonder if viewers may find David Tennant maybe a little too self-assured in the role of the French army officer.
Incidentally, by coincidence, I happened to watch the day after the film 'The King's Choice' which is an account of how Norway was brought into the war in 1941 which involved an ultimatum put to the then king of Norway by a German envoy to co-operate with the Nazis on the pretext that Britain had plans to invade! If you are interested in this general War theme of diplomacy and espionage you could watch this next.