 No one has ever escaped from Stalag 17, a POW camp for American airmen near the Danube. Maybe that s because there s a spy in barracks four. The German guards seem to know everything that s happening before it happens. Most of the American POWs suspect Sergeant J.J. Sefton, whose wheeling-and-dealing rates him special privileges from the camp guards. When Lieutenant Dunbar arrives at the prison camp, and is accused of blowing up an ammunition train, the American prisoners must expose the stoolie before he informs the Germans where Dunbar is hiding, AND get Dunbar out of the "unescapable" camp before the SS arrives to take him into custody.