La volée captive (1962)

Original title: Пленено ято

In this routine World War II drama by Bulgarian director Doutcho Mundrov, a group of doomed POWs work together to keep their own dignity and ethical standards high. As the prisoners interact against a background of strife, imprisonment, and references to a rising Communist presence, they come to discover that there is an outside informer passing on information to the enemy. Although they face impending execution, they decide to take steps to end the informer's career.