Stalag 17 is a German prisoner-of-war camp situated somewhere along the Danube River. Amongst its many captives are 640 American airmen. On “the longest night of the year” two prisoners try to escape through a tunnel but are shot by waiting guards when they emerge outside the barbed wire fence. The other prisoners conclude that one of their own must have told the Germans, and suspicion falls on J. J. Sefton, an enterprising cynic who barters openly with the German guards for eggs, silk stockings, blankets and other luxuries, and organises various other profitable ventures, though of course he denies being a traitor