Warsaw, December 1945: the Second World War is finally over and Mathilde is treating the last of the French survivors of the German camps. When a panicked Benedictine nun appears at the clinic one night begging Mathilde to follow her back to the convent, what she finds there is shocking: a holy sister about to give birth and several more in advanced stages of pregnancy.

Poland, December 1945. World War II is finally over but the country is still beset by danger. French Red Cross doctor Mathilde is treating the last of the survivors from the German camps when a panicked Benedictine nun arrives at the clinic imploring Mathilde to follow her to the convent, where she discovers a shocking scene: several holy sisters in advanced stages of pregnancy. Bound by a volatile secret, Mathilde enters the sisters' fiercely private world, dictated by order and ritual and overseen by the strict Mother Superior. Facing the hostilities of the occupying Soviet army and an unprecedented crisis of faith, the nuns increasingly turn to non-believer Mathilde as their beliefs and traditions clash with the harsh redlities of a war-torn land.