The Accursed (1957)

Every year, Colonel Price holds a reunion dinner at his English house for the members (mostly German) of the anti-Nazi resistance group he co-ordinated during the war. He took over the group in 1943 when the man who founded it was murdered by the Nazis. But now he has learned that his predecessor was betrayed by someone in the group, and he intends to devote this year's reunion to finding out who it was.