In his library, the Marquis de la Force talks worriedly with his son, the Chevalier, about Blanche, his impressionable daughter who is unable to overcome her fear of life. She suddenly appears, frightened by hostile crowds that surrounded her carriage on her way home. After retiring, Blanche returns, having been terrified by a servant’s shadow, and announces her wish to become a nun.

Several weeks later, at the Carmelite convent at Compiègne, Blanche comes for an interview with the prioress, Madame de Croissy, a woman debilitated by a fatal illness. Gently but firmly the prioress makes it clear lo Blanche that the convent is a house of prayer, not a refuge in which heroism is facilitated: it will test her weaknesses, not her strengths.

While doing their chores in the convent workroom, Blanche and Constance, a lively novice, discuss death. Constance believes she will die young and that Blanche will die with her. Blanche angrily accuses Constance of evil thoughts.

The prioress lies on her deathbed in the infirmary. Her struggle to appear calm slowly fails as the anxiety of her condition overtakes her: years of meditating on death have not made the actuality less frightening. Mother Marie accepts charge of Blanche from the prioress, who advises firmness, judgment and character – qualities she says Blanche lacks. When Blanche comes, the prioress tells the girl of her special concern for her as the newest member of their order. Saying farewell, she offers her own death to avert the dangers facing Blanche. A physician comes and goes. The prioress grows delirious, relating a fitful vision of their convent desecrated. In a last attempt to confess her fear of death, she falls back lifeless. Blanche kneels, sobbing.

In the chapel, where the prioress lies in state, Blanche and Constance intone a Requiem. When Constance leaves, Blanche attempts a prayer but flees in fear. She is stopped by Mother Marie, who gently rebukes but reassures her.

Constance explains to Blanche that the prioress died another person’s death, that her death was too ugly and hard for her. Someone else, she says, will be surprised to find death so easy.

In the chapter room, there is a ceremony of obedience. The new prioress, Madame Lidoine, addresses the sisters, counseling patience and humility, warning of the temptation of easy martyrdom. Mother Marie leads the prayer.

The Chevalier visits Blanche before escaping abroad, asking that he return and stand by their father, who is now alone. Blanche brusquely refuses, explaining that her highest duty is to the convent that has changed her life. Later, Blanche regrets her outburst, but Mother Marie reassures her that the motive behind her pride will give her strength.

Autumn 1792. The Chaplain, banned by the revolutionaries from his clerical duties, performs a last mass in the sacristy: the sisters sing an Ave Verum Corpus. Madame Lidoine observes that when there is a shortage of priests there is an abundance of martyrs, whereupon Mother Marie suggests the Carmelites offer their own lives. But Madame Lidoine replies that martyrs are chosen only by God’s will. An angry revolutionary mob storms the convent, and a Commissioner reads a decree evicting and dissolving the order. Shaken by the shouts of the crowd, Blanche drops and breaks the figurine of the Christ child.

While the new prioress is away in Paris, Mother Marie again suggests the Carmelites take a vow of martyrdom. A secret ballot reveal one dissenter. Though the sisters suspect Blanche, Constance confesses and reverses the vote, taking the vow with Blanche, who then runs off.

Working as a servant in the Marquis’ ruined library, Blanche is sought out by Mother Marie in civilian dress. The older woman urges her to return to the order, but Blanche insists on staying where she will be safer, revealing that her father has been guillotined.

In a street near the Bastille, Blanche learns from an old woman from Compiègne that the nuns have been arrested.

At daybreak in prison, the nuns’ death sentence is read. The prioress puts them under a final oath of obedience. Though the others laugh, Constance has dreamed that Blanche will return.

Meeting the Chaplain, Mother Marie learns of her sisters’ condemnation: they are lo die immediately. She despairs at not being with them.

ln the Place de la Revolution, the Carmelites advance to the scaffold, led by Madame Lidoine, singing the Salve Regina as an eager mob murmurs. The Chaplain, in plain clothes at the front of the crowd, secretly gives each nun absolution as they pass. Constance, last in line, is radiant when she sees Blanche emerge from the throng to join her sisters in death. One by one, the voice of the Carmelites are cut short by the stroke of the guillotine. The crowd disperses wordlessly.