This site gives a synopsis:
February, 1942. A Luxembourg priest is released from the Dachau concentration camp and sent home. The Nazis, annoyed with the bishop of Luxembourg's refusal to co-operate, plan to use him to give public support to Hitlers policies. Gebhardt, a superior officer in the Gestapo, gives Kremer nine days to make a decision. If he refuses their offer, he will immediately be sent back to the camp.
I very much enjoyed this film, and highly recommend it.
So too does Stephen Greydanus, the National Catholic Register's film critic, whose review is here.