Classic wartime propaganda thriller based on a short story by Graham Greene. During the Second World War, a platoon of German paratroopers plan to place a signalling device in an English village in preparation for an upcoming invasion. Disguised as British troops, all goes according to plan until vigilant local postmistress Mrs Collins (Muriel George) has her suspicions aroused by some clues left by the Germans.
Unfortunately, respected villager Oliver Wilsford (Leslie Banks), the man who she informs of her suspicions, is actually a fifth columnist in league with the enemy. With the Germans now aware that the game is up, they quickly revert to their back-up plan and take the entire village hostage. As they try to maintain an appearance of normality in the village, the Germans soon find themselves beset by the heroic attempts of the villagers to raise the alarm to the outside world.