The Marquise of O—— is a novella by Heinrich von Kleist first published in 1808. It narrates the story of a daughter of the Commandant of a castle, the widowed Marquise of O——; she is assaulted by a group of Russian soldiers attacking the city in Northern Italy but is eventually rescued by the Russian Count F——. The Count brings the woman to the part of her father's castle unaffected by the fire.

The morning after the tumultuous events, the Commandant's family cannot thank the rescuer enough, and to the Marquise herself he appears as an angel from heaven. Count F—— makes a proposal to the Marquise, but the family is daunted by such rashness on the Count’s part. That is why her parents take their time to ponder his proposal. Meanwhile, evidence that the Marquise is pregnant comes to the surface, even though she has not been with a man since her late husband's death. Apprehensive of dishonor, the family deprives her of her title and banishes her from home.

A woman of chastity, dignity and integrity, the Marquise doubts the obvious. She bids the attending doctor be gone, thinking him a slanderer. Then she turns her thoughts to mysterious incomprehensibility of the world and even to mystical associations such as immaculate conception.

The Marquise, who was about to swoon again, drew the midwife down to her and laid her violently trembling head on her breast. In a faltering voice she asked her how inflexible the laws of nature were: was it possible to conceive without one's knowing it?

Although banished, the Marquise refuses to abandon her children and leaves home with a sense of liberation.

Having learned how strong she was through this courageous effort, she was suddenly able to raise herself, as if by her own bootstraps, out of the depths into which fate had cast her. . . . Her reason, which had been strong enough not to crack under the strain of her uncanny situation, now bowed before the great, holy and inscrutable scheme of things.

The desperate Marquise's last resort is to publish in the local newspaper an appeal to the unknown father of her unborn baby. She asks him to come forward. The next issue of the newspaper contains his response. The father is ready to appear before the Commandant. At the appointed time, the same Count who seemed an angel to the Marquise comes to the Commandant's house.

This time, the Count appears as a devil to the Marquise. It becomes obvious to her that the Count dishonored her, taking advantage of her unconscious state while the castle was being stormed. Yet he reaffirms his proposal to her, offering to redress the grievance by marrying her.

Being truly in love with the Marquise, the Count treasures her image in his heart while he looks death in the face. The Count's marriage proposal is not just to save the Marquise from dishonor. It is a matter of his own relief.

. . . it was impossible for him to go on living any longer without a clear understanding about something that was absolutely necessary for his soul's peace.

After the hurried wedding, the Marquise tries to keep the Count at bay. However, time heals all wounds, and after their first child is born, "a whole line of young Russians now followed the first."