The River Line(1964)

Original title: Kennwort... Reiher

France 1944: American pilot Philip Sturgess is shot down but found by a resistance group. In the neighborhood Sturgess meets another American and shortly thereafter the British Major Barton, called “Reiher”. He claims to have fled a German prison camp. Shortly before leaving for Spain to escape the Nazis, Sturgess discovers that Barton has written a letter to Germany. This confirms the suspicion that he could be a German spy…