The novel opens in Paris in May 1868. Christopher Newman, a wealthy American businessman in his mid-thirties is visiting the Louvre museum, but becomes overwhelmed by the number of paintings he is seeing. He notices a young woman making a copy of one of the paintings and strikes up a conversation with her, offering to buy the copy. The young woman, who is named Noemie Nioche, persuades him to pay a high price, and also introduces him to her father, who offers to give Newman French lessons. After the father and daughter depart, Newman runs into a fellow American, Tom Tristram, who he had befriended during the war. Newman explains to Tristram that he has made a fortune for himself through hard work and enterprise, but is now focused on enjoying himself. Tristram introduces Newman to his wife, and he confides to them that he is seeking to marry. Mrs Tristram mentions a friend of hers, a young widow named Claire de Cintre who comes from a very old and aristocratic family, and praises her very highly. A short time later, he visits the Tristram family again, and finds Madame de Cintre there on a visit. Intrigued, he goes to her family home to visit her, where he meets her two brothers. The younger, Valentin, is kind, but the older, Urbain, is reserved and tells Newman that Madame de Cintre is not at home.
A short time later, Monsieur Nioche comes to deliver the painting to Newman. While there, Monsieur Nioche expresses his concern about his daughter's ability to marry, since he is unable to provide her with a dowry, and Newman offers to buy additional paintings, thereby financing her dowry. Noemie and Newman meet at the Louvre so that he can select the paintings he would like her to copy, but she frankly tells him that she is an unskilled artist and he is wasting his money. She also admits that she is not interested in simply finding a stable match; she has ambitions about marrying very well.
Since Madame de Cintre is spending the summer in the country and is not available to spend time with, Newman spends the summer months traveling, returning to Paris in the autumn. Mrs. Tristram tells him that Madame de Cintre is unhappy but required to be subservient to her family. He goes to visit her again and gradually becomes acquainted with her and the rest of the Bellegarde family: her elder brother Urbain and his wife young Madame Bellegarde, her rakish younger brother Valentin, and her strict, aloof mother, old Madame Bellegarde. He becomes quite close with Valentin, but when he explains to him his hopes of marrying Madame de Cintre, Valentin is surprised and convinced that the marriage will not be possible, since, despite his wealth, Newman is not an aristocrat. Despite this, Newman is determined to woo Madame de Cintre and proposes to her. She rejects him, claiming she does not intend to remarry, but agrees to continue to spend time with him if he does not speak of a romantic future for at least six months.
Newman's commitment to winning Claire's heart is strengthened as he learns her history from Valentin. She was forced into an unhappy marriage with a wealthy man at a young age. After his death, she learned that he had acquired his money as a result of questionable business practices. Horrified, she refused to claim her inheritance from him. Her family opposed this choice and Claire finally struck a bargain, agreeing to ten years of total obedience in exchange for rejecting the fortune, with the only exception being that she cannot be forced to marry. Relations are also tense with her family, who disapprove of him as a self-made man, but are also intrigued by the wealth he has.
Monsieur Nioche comes to visit Newman, and expresses his anxieties that Noemie is not progressing with her paintings. Newman agrees to go to the Louvre to check up on her progress, and while there, he runs into Valentin, which results in him introducing his friend to the young woman. Valentin is attracted to Noemie, and excited about the idea of pursuing her. After a time, Newman is formally accepted as a suitor to Claire. He also encounters Mrs. Bread, an English servant who has worked for the Bellegarde family for more than 40 years, and Lord Deepmere, an English lord who is a distant relation of theirs, come to France to visit. When the six months have elapsed, Newman again raises the question of marriage to Claire, and this time she accepts his proposal.
While Newman is elated about his engagement, the Bellegarde family reacts coldly to the news, with the exception of Valentin. Newman hopes to throw a party to celebrate the engagement, but Madame Bellegarde insists on doing so first. Meanwhile, Newman hears that Noemie has left her father's house and been installed as the mistress of a wealthy man. Monsieur Nioche stops visiting Newman, and Newman, worried, tracks him down at his local café, where he is surprised to find both father and daughter together. Noemie is unashamed that she is advancing her position through her sexuality, and while her father claims to object to her behavior, he also willingly takes money from her. Despite this, Valentin also continues to visit her, and finds himself melancholy due to his attraction to her.
The ball celebrating the engagement takes place with great splendor. Newman basks in his sense of triumph at securing Claire's hand, giving little thought to the fact that he surprises both old Madame Bellegarde and then Claire herself in intense conversations with Lord Deepmere. Shortly after the party, Newman is attending the opera on a night that Urbain, his wife, Valentin, and Noemie are all also present. Noemie is being courted by a young German man named Stanislas Knapp. During the course of the opera, Stanislas and Valentin get into a quarrel and agree to a duel to settle their honor. Newman is nervous about this, but Valentin seems calm, and leaves for Switzerland, where the duel is to take place.
The next day, when Newman goes to visit Claire, she is packing to leave for the country, and tells him she cannot marry him after all. Her mother and brother admit that they have pressured her to give him up, since they think the marriage is beneath her. Frustrated and hurt, Newman confides in Mrs. Tristram, who suggests that the Bellegarde family may hope to have Claire marry Lord Deepmere instead. Newman then receives word that Valentin has been seriously injured in the duel, and hurries to Switzerland to be by his side.
Newman finds Valentin close to death, and only reluctantly shares the news that his engagement has been broken off. Valentin apologizes for the behavior of his mother and brother, and just before he dies, he advises Newman to ask Mrs. Bread about a dark family secret that she has knowledge of. Shortly after the death, Newman visits Claire at her country estate and tries again to persuade her to marry him, but she refuses and tells him that she plans to become a nun. Newman then speaks with Mrs. Bread, asking about the family history. Mrs. Bread explains that when Claire's first marriage was being arranged, she was very unhappy, and her father, the old Marquis Bellegarde, tried to support her. In order to ensure the marriage took place, Urbain and his mother killed him. Shortly before he died, the old Marquis wrote a note stating the cause of his death. Mrs. Bread has kept it secretly ever since, but she gives it to Newman.
After returning to Paris, Newman confronts Madame Bellegarde and her son, threatening them with the note. They are stunned, but maintain their composure. The next day, Urbain comes to visit Newman to find out what it would take to ensure his silence. Newman asks for Claire but Urbain refuses, and the two part without coming to an agreement. Newman's initial plan is to cause a scandal by revealing the crime of the Bellegardes to their social circle. He goes to visit the Duchess D'Outremont with the intention of telling her, and then abruptly decides his plan is foolish. Instead, he goes to London. While there, he runs into Monsieur Nioche and Noemie, who is now having an affair with Lord Deepmere. Afterwards, he returns to America, where he restlessly travels between New York and San Francisco. There, he receives word that Claire has taken her final vows. He immediately returns to Paris, ad goes to the convent, only to realize that he has no way of accessing Claire, and will never see her again. Back at the Tristram house, he burns the confession.