After the evacuation at Dunkirk June 1940 some thousands of British prisoners are sent to German P.O.W. camps. One such group includes "Capt. Geoffrey Mitchell" a concentration-camp escapee who assumed the identity of a dead British officer. To avoid exposure "Mitchell" must correspond with the dead man's estranged wife Celia. But eventual exposure seems certain and the men must find a way to get him out. If he reaches England though what will his reception be?