In preparing for a secret raid on a German-held French coastal village, a British security officer is chosen to monitor activities in England among army personnel of the 95th Infantry as well as civilians with whom they mingle. At the same time, German intelligence send Agents 23 and 16 to England to obtain information from sources including conversations overheard in pubs, railway stations, shops and other public places. Agent 16 is caught, but 23 reaches his contact, Mr Barratt, a bookseller at Westport, who assigns him the job of infiltrating an ordnance depot.
The scenario involves covert operations, intelligence gathering, and infiltration tactics used by both British and German forces during World War II.