When a Benedictine nun explains to an atheist the mechanics of faith among even the most faithful in The Innocents, she says, “Behind all joy lies the cross.” Although it’s a truism that applies not only to spiritual devotion but to all kinds of love, in director and co-writer Anne Fontaine’s film, it’s an especially powerful sentiment that’s gripped a cloistered convent under the care of a French doctor in 1945 Warsaw. The doctor had been begged to sneak away from her Red Cross station aiding Polish survivors to attend to the French convent, in which many sisters are pregnant and about to give birth.

These pregnancies are not the result of immaculate conceptions. Rather, they’re the aftermath of a nightmarish attack by the Red Army. Not only were the sisters’ bodies and minds violated, their very beliefs—the beliefs they’ve dedicated their lives to—suddenly wobbled. It wasn’t an automatic admittance; in fact, when the doctor, Mathilde (Lou de Laâge), first showed up to help a nun in labor, she was practically turned away. The nuns’ attitude was difficult to understand. Why, after Mother Abbess (Ida’s Agata Kulesza, steely) allowed Mathilde to perform a Caesarean on a sister in labor, was she ordered not to come back to see after mother and child? And what about the other women about to deliver?

The nuns’ vows include not showing their bodies to anyone nor letting another person intimately touch them. And thus the pregnant sisters preferred to scream and squirm throughout labor, indeed even trying to keep their babies from being born, instead of allowing Mathilde to help save the lives of both the mothers and their children.

Fontaine adapted The Innocents (along with four others) from the diary of a real-life Mathilde. After the director’s embarrassing misfire 2013’s Adore—a quite serious version of the Saturday Night Live digital short “Motherlover,” though the subject is their only connection—this film is a veritable triumph. Boasting the mysteries and themes of Ida regarding tight-lipped religion and the clash of faiths, The Innocents pulls you into a world behind walls in which reason exists, though not always according to layman’s logic.

Baby after baby is snatched by Mother Abbess and allegedly taken to a big-hearted acquaintance willing to raise the children. Throughout the film, there are lies of omission; then there are straight-up lies. This turns out to be one of the latter, unsurprising if you consider that every traditional storytelling arc must have a conflict.

When Mathilde’s quick thinking spares the nuns from yet another invasion, the sisters are as giddy as children, thanking her and asking her to stay. This isn’t the only bright spot in what’s a largely sober tale, however—shame and mourning are kept at bay while the nuns’ vows extend to include service. This evolution of the convent, and the boost of the community around it, would not have been possible if not for a doctor without borders.

The Innocents opens today at Landmark Bethesda Row.