It’s an interesting war-themed film, primarily due to its subject matter rather than any unique aspects of the plot – the central puzzle is fairly standard. Richard Greene portrays "Bob Randall," a journalist returning from Dunkirk and determined to look into British pacifists who might be vulnerable to German spies. Alongside reporter "Carol Bennett" (Valerie Hobson), he begins an inquiry that quickly reveals the potential danger. The film presents a more realistic portrayal than many others; seeing people genuinely scared in underground stations while bombs fall above does convey their situation and the dangers of possible defeat, as they likely experienced in London during 1942. A dependable group of actors helps to maintain the suspense, although it occasionally feels like a stronger – almost propagandistic – caution against yielding to aggression than a standard movie.

Source on TMDB