Lots of slogans such as "Be like Dad, Keep Mum" and "Keep it under your Hat" are visible on the walls in various scenes to reinforce the plot of this British wartime movie illustrating how gossipy talk can result in unknowingly giving valuable information to Nazi spies.
This isn't so much an action film, as a series of scenarios that convey a message to the watching public that "careless talk costs lives". It started out life as a training film and you can tell by the rather clunky editing that director Thorold Dickinson was thinking on his feet as this project aimed at the military grew into a very important, and effective, counter-espionage tool. It's got quite a formidable cast of serving (or reservist) soldiers including Mervyn Johns, Jack Hawkins, Stephen Murray, Basil Sydney as well as Torin Thatcher in his typical role as the baddie; and the narrative weaves threads that cleverly expose just how easily the enemy got hold of information and capitalised on it. It uses actuality from time to time, and has a strange sort of excitement especially as the climaxes to each thread are not always favourable to the British which also lends it a considerable authenticity. There is a bit of wartime black humour to enjoy too, and though a curious film to watch, it has an unique plausibility which I found interesting, and to an extent, quite enjoyable.