A young French idealist (John Clements), who gives his name as Jean Baptiste, arrives in “St Pierre-le-Port”, a small town near Saint-Nazaire, a major port and base of operations for the German Navy, particularly their U-boats, on the Atlantic coast. Baptiste tells a member of the French Resistance that “I come from Saint-Nazaire. I’ve details of the submarine base, the docks and power plant. If I can get them to England…”
The first half of the film often has a light-hearted tone; the Germans are portrayed as bumbling and easily outwitted. The German commandant is overweight and gullible. However, after the Resistance successfully sabotages a German armaments train, the SS take charge of the town, and the occupation takes a brutal turn.