The wealthy Alovisa is madly in love with the attractive war hero Count D'Elmont, but because of a custom that forbids women to confess their love to a man without his proposal, she must find another way to do so and writes him an anonymous love letter with the suggestion that he will recognize her as his admirer at the next court ball. There, D'Elmont believes the lovely Amena to be the sender and embarks on an affair with her, which for him is only an erotic adventure, but for her the beginning of a deep romance.
Alovisa, who is friends with Amena, is aware of this affair, so she sets out to get rid of her rival. A coincidence convenient for her causes D'Elmont to take Amena to Alovisa's house in the evening so that she can recover from a swoon she had fallen into for fear of being confronted by her strict father after a clandestine romantic rendezvous with D'Elmont.
When he is about to leave, she asks D'Elmont to give her back a letter she had written to him. By mistake, he confuses this letter with Alovisa's letter, which thus falls into Amena's hands. When she reads it later in the guest room and recognizes Alovisa's handwriting, she is shocked because she recognizes her friend as her fiercest rival and believes that D'Elmont is having a second love affair with Alovisa.
Meanwhile, Alovisa has summoned Amena's father, Monsieur Sanseverin, who is in anxiety about his missing daughter. Alovisa informs him about his daughter's affair with D'Elmont and suggests that he send Amena to a convent until she gets over her love for D'Elmont, which he agrees to do. Amena also consents the next day, because she is so disappointed by D'Elmont's supposed duplicity that she gladly would flee from the false world to a convent.
D'Elmont is not unhappy with this outcome when he learns of it, and is open to the idea of marrying Alovisa, about whose love for him he is now in the know, while he loves only her wealth. He learns from his brother, the Chevalier Brillian, who has come to Paris, that he is in love with Alovisa's sister Ansellina and wants to marry her. Now D'Elmont decides to marry Alovisa secretly so as not to offend Amena, who is about to leave for the convent.
Not long after the wedding, D'Elmont learns that his former guardian, Monsieur Frankville, to whom he is bound in gratitude, is dying. He rushes to see him and meets Frankville's daughter, the young and beautiful Melliora. For both it is love at first sight. D'Elmont has to promise the dying old man to take Melliora in as his ward, which he accepts. After Melliora is lodged in his house, D'Elmont realizes that a profound inner change is happening to him; for the first time he is deeply in love and regrets being bound to a woman he married only for her money.
Then a letter from Amena reaches him from the convent, in which she showers him with reproaches and at the same time professes her love. Since she seems to expect an answer, D'Elmont writes a letter in which he expresses his regret and also hints that he is not happy with his current marriage. In doing so, he is secretly observed by Alovisa, who persuades the servant in charge of delivering the letter to hand it over to her. She is furious at the contents, but decides not to let her husband know. So D'Elmont hides his love for his ward Melliora, Melliora hides her love for her guardian D'Elmont, and Alovisa hides her jealousy and her anger at her husband. However, D'Elmont and Melliora clearly sense that the other reciprocates the feelings.
After Monsieur Frankville's funeral, D'Elmont is given a letter from Amena, which reveals that she did not receive D'Elmont's letter. Moreover, she has become a nun forever through a vow out of disappointment over the missing answer. The Count then confronts the servant, dismisses him, and goes to Alovisa, whom he angrily reproaches for her jealousy, but who vigorously defends herself. Afterwards, D'Elmont sees Melliora reading a book in the garden, is again seized by love, and, recognizing the book as a work by the philosopher of science Fontenelle, argues that this Enlightenment mind would have written not about science but about Melliora's beauty had she been known to him. He then embraces Melliora, who, torn between virtue and loving desire, tears herself away from him in order to maintain the appearance of virtue. Now it is finally clear to both of them how much they love each other.
As a result, Melliora avoids situations in which she would be alone with D'Elmont in order to better suppress her passion. He, in turn, suffers a lot from not being able to express his passion openly. Alovisa worries about his health and suggests a joint trip to the Count's country estate. With difficulty, he manages to persuade Melliora to go along.
Once there, they are all invited by D'Elmont's friend Baron D'Espernay to a party. To the amusement of the guests, D'Espernay's fun-loving sister Melantha recites love poems from a book, which the hitherto silent Melliora takes as an opportunity to argue with eloquence against a free approach to love and the danger of effeminate pleasures, so that everyone comes to the conclusion that she was born only to arouse desire without being susceptible to it herself.
A few days later, the Count has the opportunity to have a longer conversation with his beloved about love and passion. However, his arguments fall flat on their face, as Melliora insists that uninhibited love can all too easily lead to ruin. Nevertheless, his passionate declaration of love triggers in her not only virtuous defenses but also, once again, desirous feelings, something that no one but D'Elmont has ever achieved with her.
When the Count tells his friend D'Espernay about his love, the latter makes fun of him and urges him to seduce Melliora, because her virtue was only the product of education, but in truth she was desiring sensual pleasure. D'Elmont is persuaded and decides to seduce Melliora with the Baron's help as soon as possible.
A few days later, the Count makes his first attempt and enters her room at night when she is asleep. As he bends over her, she wraps her arms around his neck in a dream and confesses her love, and when she awakens, her resistance is only half-hearted, so D'Elmont is about to conquer her when there is a knock at the door, so he leaves the room through a back door. It turns out to be Melantha and not Alovisa, as the two initially feared.
Meanwhile, the deceitful D'Espernay, who is silently in love with Alovisa, has devised a plan to break her and D'Elmont up so that he can win her over. Knowing that Alovisa suspects her husband of having a mistress, he proposes to show her the mysterious lady being intimate with D'Elmont after the ball to which he wants to invite her, D'Elmont and Melliora. At the same time, he hints at wanting to receive certain favors from Alovisa as a reward afterwards. Alovisa makes a pretense of accepting the deal because she is desperate to find out the secret of her husband.
In parallel, the Baron agrees with D'Elmont to assign Melliora a specific room for the night of the ball, where he can seduce her undisturbed after the ball. His plan is to lead Alovisa to this room so that she will catch her husband in adultery. D'Espernay, however, makes the mistake of tasking his sister Melantha with assigning specific rooms to Alovisa and Melliora, for Melantha suspects what her brother is planning and decides to assign Melloria her own room so that she herself will be in bed in the room where the Count, whom she desires sexually, will appear that night.
After the end of the ball, when the guests have left or gone to bed, the Baron leads the Count to the supposed room of Melliora. Without lighting a candle, D'Elmont slips into bed, believing he is dealing with his beloved, who offers surprisingly little resistance to his advances. While they are having sex, Alovisa suddenly appears at the door with a lighted candle, led there by the Baron, and throws a tantrum. Melantha has immediately hidden herself under the covers, so that neither the Count nor Alovisa recognize her. The Baron also comes over and pretends to be surprised. Then Alovisa faints with rage and is carried to her room to recover by servants who have come running. When Melliora appears at the door, D'Elmont is thunderstruck and finally discovers that it is Melantha with whom he has slept.
The Count is now disgraced in all directions, Melliora is angry, and the Baron is seething with anger at his sister for screwing up his intrigue. After bringing D'Elmont to his room, D'Espernay visits Alovisa, who has recovered, and intends to continue his intrigue. After all, she does not know who the woman in the bed next to D'Elmont was, and urges him again to reveal the name. He shows readiness, but insists on a demonstration of her favor beforehand. In the end, Alovisa refuses, and the Baron maliciously says that the Count will just continue to have fun with his mistress.
A few days after the return of D'Elmont, Alovisa and Melliora, Alovisa changes her mind and summons the Baron. She implores him to reveal the name, he in turn makes her favor a condition. Finally, she promises to grant him this favor if he stays as a guest and visits her at night in a certain chamber. Then she goes to Brillian, who has come to visit with Ansellina in the meantime, and asks him to be secretly present in the chamber in order to save her from the importunate Baron. Brillian is surprised that his brother should have a mistress, but is willing to comply with the request.
Since Melliora has overheard their conversation, she knows the danger she is in and asks the Count, without giving the reason, to visit her in her chamber that night to discuss the situation with him. Shortly after he appears there, they hear screams and the clashing of swords. D'Elmont runs in the direction of the sounds with his sword drawn, but the hallway is so dark that he bumps into someone, who then falls to the floor. As Melliora comes after with a candle, they see that at the Count's feet lies Alovisa, who had run into her husband's sword and is now mortally wounded. Then the Baron comes running up, pursued by Brillian, and sinks to the ground beside Alovisa, also wounded. The doctors to whom Brillian has the two wounded brought are unable to save Alovisa, and D'Espernay also dies two days later as a result of the injury Brillian inflicted on him in the sword fight.
A report is compiled from witness testimony and presented to the king. D'Elmont and Brillian are acquitted, as Alovisa's death is considered an accident and D'Espernay's death justified. Melliora, racked by feelings of guilt, retires to a convent; Brillian finally marries his Ansellina; Count D'Elmont, highly depressed by the death of Alovisa and Melliora's withdrawal, leaves his brother in charge of his estates and decides to turn his back on Paris forever and travel to Rome, accompanied by two servants; Melantha takes a husband and, seven months later, gives birth to a child, who is, of course, D'Elmont's.
In Rome, the Count avoids, as far as possible, any social life. That he is still alive at all and has not laid a hand on himself is probably due to the efforts of his brother, who has persuaded Melliora to regularly exchange letters with D'Elmont which is now his only consolation and hope. Of course, he is admired from afar, as he was in Paris, by many noble ladies, but does not answer a single one of the letters they send him. A lady, however, remains persistent and immediately sends a second one behind, in which she strongly reproaches him for his stubbornness. He gives the messenger a reply letter in which he justifies his attitude with sadness.
After attending a mass in St. Peter's, he encounters a beautiful woman who seemingly unintentionally drops an amulet, which he brings after her. D'Elmont does not yet know that this is Ciamara, who is insanely in love with him. The following evening he sees three bandits fencing against a nobleman in the dark street, whom he rushes to help with his sword. He draws two of the attackers on himself, while the nobleman is able to draw his pistol and shoots the third. The other two then flee, and the nobleman angrily chases after them without thanking the Count, who sees a piece of the nobleman's broken sword lying on the ground and puts it in his pocket. Then he moves away from the scene, because people are approaching and he does not want to be arrested as a murderer.
The next morning he is visited by a handsome young man who identifies himself as Monsieur Frankville junior, Melliora's brother. He is very angry and wants to challenge the Count to a duel for allegedly ruining his sister's reputation. D'Elmont maintains his innocence. Then Frankville sees on a table the piece that had been cut off his sword in the fight the day before, and finds out that it was the Count who saved his life. Now he begins to see in him a friend and shows him the letter that had incited him against D'Elmont. After D'Elmont tells him his story, Frankville makes him familiar with his own adventures in Rome. A rich Roman, Signore Cittolini, had taken a fancy to him and wanted to win him as a son-in-law by marrying his daughter Violetta. However, Frankville was not in the mood for marriage at that time. Cittolini himself was eager to marry Camilla, the stepdaughter of his sister Ciamara, who tried to blackmail Camilla into marriage by threatening to send her to a convent if she refuses. But since Cittolini has a bad character and is very unprepossessing, Camilla was averse to that marriage.
When Frankville saw Camilla for the first time in Cittolini's garden, he was instantly smitten. During another encounter it became apparent that she was also in love with him. So Frankville overcame his misgivings about betraying Cittolini and began a sexual affair with Camilla that was accompanied by rising love. However, Cittolini found out about it, forbade Camilla any contact with her lover and threatened Frankville with revenge and also sent the three bandits after him, from whom D'Elmont had saved him the day before.
Having listened to the story, the Count proposes to deliver in his own person a message from Frankville to Camilla, who immediately draws up a love letter. So D'Elmont goes to the house of Ciamara, where Camilla lives, and is led to a lady who receives him with a veiled face and whom he believes to be Camilla. She pays little attention to Frankville's letter, but quickly proceeds to showering D'Elmont with declarations of love. When she removes her veil, he recognizes the beautiful woman he has seen several times before, without knowing her identity. He only realizes later that she is Ciamara, pretending to be Camilla. Now he thinks the woman is a hypocritical traitor, tells her that he is already in love with another woman, and leaves the room as she faints in despair at his rejection.
He reports Frankville about this, who distrusts him as much as his supposedly unfaithful lover and sends Camilla a letter expressing his disappointment and granting her freedom to find other lovers. After that, a letter arrives from Camilla reiterating her love for Frankville. Both are stunned by this apparent height of hypocrisy. D'Elmont's attempt to talk Frankville out of his love for Camilla, however, does not bear fruit. Not long after, a letter arrives to D'Elmont from Ciamara, in which she declares her love for him and clears up the misunderstanding about Camilla. Frankville is hugely relieved, but now has the problem that his angry letter to Camilla has already been sent.
So he asks the Count to go back to Ciamara under a pretext and take him along as an unrecognizable disguised servant so that he can secretly visit Camilla. While Frankville waits in an antechamber, D'Elmont is led to Ciamara and converses with her in order to gain time for his friend. The latter threatens the servant with his pistol and forces her to bring him to Camilla, who, however, is still severely disappointed by Frankville's recent mistrust, and when he turns his pistol on himself to put emotional pressure on her, she snatches it from his hand and throws it out the window. A shot is released from the pistol, whereupon a group of servants rush in and fight Frankville with clubs and sticks, while he fights back with his sword. D'Elmont also comes over, alarmed by the noise, and helps his friend with his sword to fight off the servants until they escape.
Some days later, D'Elmont receives a letter from Cittolini's daughter Violetta, warning Frankville against further revenge from her father and offering her help in mediating with Camilla. She names St. Peter's as meeting place after the next mass. There, the two give Violetta a letter from D'Elmont for Camilla, in which he declares himself the sole culprit for the misunderstanding. The Count does not fail to notice that Violetta loves him passionately, which makes him uncomfortable because, as his experience shows, this does not end well for the respective woman in love.
At the next meeting, Violetta tells them that Camilla is ready for reconciliation and a secret meeting. But then a letter arrives from Brillian, revealing that Melliora was kidnapped from her convent by unknown men shortly before, which shows that the letter from Sanseverin was full of lies. D'Elmont is beside himself with worry. After secretly contacting Camilla, the three decide to flee Rome together, D'Elmont's main concern being to follow possible traces to Melliora from Paris. The group is joined by a young page named Fidelio, who shows the Count a letter of recommendation from Violetta. As it turns out later, Fidelio is Violetta herself in boy's disguise, who in this way wants to stay in touch with her beloved D'Elmont, of which Camilla is in the know. After a few days of many detours to escape from possible pursuers, they are caught up by a stranger who informs them that Ciamara has drunk poison out of lovesickness and that Cittolini has died of grief, because he lost Camilla and his sister Ciamara, and because Violetta has disappeared. Fidelio/Violetta then falls ill, feeling guilt over their deaths.
A thunderstorm forces the group to ask the hospitality of a house where the Marquis De Saguillier lives. They are received kindly, Fidelio is put in bed to recover, but his/her condition is very serious. At night, a young woman appears in D'Elmont's room, who, to his infinite surprise, turns out to be Melliora, abducted to this house because Saguillier loves her beyond measure, but who, apart from the violent kidnapping, has treated her respectfully. They discuss a plan to get Melliora away from the Marquis without leaving behind the sick Fidelio, who is not fit to travel.
As the Marquis wants to proudly present his new bride to his guests in the evening, the travelers, except for Fidelio, gather in the salon that evening, where the Marquis calls Melliora in. Frankville, not yet informed by D'Elmont, is entirely confused by the sight. Melliora uses the general confusion - for the Marquis is also dismayed when he perceives Frankville's mimic indignation - for a speech in which she announces that she will give herself as wife to the man whom her brother, who is present, and the Count D'Elmont would appoint. Both indicate that they will use their swords if necessary. Now the Marquis realizes his hopeless situation. In the midst of the joyous reunion between Melliora and her brother, it is noticed that Camilla has disappeared. Frankville and the others learn that she has gone to Fidelio, and follow her to find that the page is dying. In her last minutes, Violetta reveals her identity and her love to the Count, who is deeply stricken with grief, as are the others.
The couple eventually decide to marry after Violetta's funeral, and are later blessed with numerous offspring.
