Hollywood made some great movies as part of the effort to win World War II. In fact, my all-time favorite movie, and one of the greatest of American movies, Casablanca, was at least in part a result of that effort.
But Hollywood also made some poor films in the same category, and this, I'm afraid, is one of them.
There's nothing wrong with the acting, though the mix of accents is disconcerting at times. Elisabeth Bergner, a Viennese whose English reminds me on occasion of Luise Rainer, plays a French aristocrat. Basil Rathbone plays a French politician. Lee J. Cobb plays a Nazi officer. Only Randolph Scott, playing an American pilot, comes off naturally as what he is supposed to be. Some of the lower-ranking Nazi soldiers sound too colloquially American. I suspect that Universal just didn't have the means to hire a more convincing cast, though Rathbone and Cobb were certainly good actors. (Rathbone was a Universal staple, since that's where he made the Sherlock Holmes movies.) As others have explained, it is basically the story of Bergner, who plays a very naive woman in love with a French politician and collaborator. She at first believes the lies he tells her. With the fall of France, she sees the light, however. Thereafter she becomes involved in a Resistance cell, and works to fight the Nazis.
The script isn't great, however, and sometimes the action seems disjointed. The end, as a previous viewer remarked, happens too fast and is not at all convincing. It's rather like the end of Mel Brooks' remake of "To Be or Not to Be," but to be taken seriously.
Some things make no sense at all. Why, for example, would Bergner's character play very dramatic classical music in a low-life bar? If you're interested in World War II movies, you might enjoy this. It's not embarrassing. It just isn't very convincing.