Set in German-occupied Paris, the plot concerns the day-to-day struggles of the French resistance during WWII, made all the more believable by a cast chosen from among real-life refugees – in other words those who were eye-witnesses to the film's historical backdrop. I suspect that when "Paris After Dark" played in small-town America, the world it unveiled was still rather exotic. Even with full-on U.S involvement after Pearl Harbor, the idea of an underground resistance for most Americans was something shadowy and obscure. New York Times reviewer Bosley Crowther, though not at all impressed, did acknowledge "the terrible tragedy of the French people under Nazi occupation" which the film evoked. However, this is a film that holds its own alongside similar portrayals of the war in Europe, such as Robert Stevenson's "Joan of Paris" and William Wyler's "Mrs. Miniver", the latter in which the inimitable Greer Garson and Walter Pidgeon bolstered the moral imperative of continued U.S. involvement.
Fans of "Casablanca" (1942) will recognize the lovely Madeleine LeBeau in a supporting role. According to Wikipedia, LeBeau, along with her husband, Marcel Dalio, escaped from Paris in June, 1940, just ahead of the Nazi advance, eventually finding their way to the U.S. Fans of George Sanders will love his role as a heroic leader of the underground movement. But the stars of the film are Brenda Marshall and Philip Dorn. Some viewers may recall Marshall as the scientist Nora Goodrich in Anthony Mann's "Strange Impersonation" (1946). The Dutch-born Dorn was better known as an actor in Germany but who also moved to the U.S. with the war's outbreak. Director Leonide Moguy sought refuge in the States in a similar manner. He also directed the interesting noir, "Whistle Stop" (1946), with George Raft and Ava Gardner before returning to France. In short, this was a cast and company that appeared to know first-hand what they were portraying during one of the war's bleakest periods.
As of this writing, it is available as a Fox Cinema Archives release, and well worth tracking down, if only for the history lesson it movingly portrays.