Frédéric Moreau watches Paris disappear as his boat heads for his childhood home, Nogent-sur-Seine. On the boat, he sees a beautiful woman, Madame Arnoux, and instantly falls in love with her. At home, he spends time with Charles Deslauriers, his best friend, who encourages him to befriend Monsieur Arnoux as a way of getting closer to Madame. He also tells Frédéric to take advantage of Frédéric’s mother’s friend Roque, who has connections to a man in high society, Monsieur Dambreuse.
Frédéric returns to Paris to attend law school and visits the wealthy Dambreuse, a banker. Dambreuse is uninterested in Frédéric. On his way home, Frédéric finds an art shop with Arnoux’s name on it. Frédéric is unhappy in Paris, stops attending classes, and drifts idly through the city. One day, there are riots in the streets. Frédéric asks a man named Hussonnet what’s happening, but he doesn’t know. An innocent-seeming man is arrested, and Frédéric and Hussonnet follow him. In jail, they visit the man, named Dussardier, but cannot help him. Frédéric finds out that Hussonnet works for Arnoux’s magazine, and he eventually takes Frédéric to Arnoux’s house. Frédéric begins spending more time with Arnoux and the men in Arnoux’s social circle, including Regimbart and Pellerin, although he never sees Madame Arnoux.
Deslauriers visits Paris, but Frédéric is invited to dinner at the Arnouxes’ house and ignores him. There, he finally sees Madame Arnoux and speaks with her. He decides to be a painter and recruits Pellerin to teach him. One day, Frédéric, believing that Arnoux is out of town, tries to visit Madame Arnoux alone. She is not there, but Arnoux is. Frédéric accidentally breaks the handle of a parasol.
Months later, Frédéric attends a party for Madame Arnoux’s name day. He gives her a new parasol, apologizing for breaking hers, but Arnoux angrily pulls him away. Arnoux gives Madame Arnoux some roses, which she throws from the carriage as she, Arnoux, and Frédéric go home, an action only Frédéric sees.
Frédéric receives a large inheritance from his uncle Barthelemy. When he returns to Paris after visiting his mother, the Arnouxes have moved and he must work to find them. Arnoux has become a pottery dealer. Frédéric vows to stop thinking about Madame Arnoux. He uses his new fortune to buy new clothes, plans to visit the Dambreuses, and then visits Arnoux instead. Arnoux takes him to a party, where he meets a woman named Rosanette. When Frédéric finally visits the Dambreuses, he is surprised at the triviality of the people there.
Frédéric has a house-warming party. The guests gossip about politics and a scandal they think Arnoux is involved with. Deslauriers asks for money to support Hussonnet’s political paper, but Frédéric refuses.
Frédéric figures out that Rosanette is Arnoux’s mistress, and he tries unsuccessfully to make Rosanette his own mistress. At a party at her house, Dambreuse suggests he might be able to get Frédéric a job in business.
Frédéric becomes close friends with both Arnouxes, earning their trust. He tries to break them up. To avoid an argument, Arnoux tells Madame Arnoux that Rosanette is Frédéric’s mistress, which Frédéric angrily denies. He helps the Arnouxes put off repaying a debt they owe to the Dambreuses. He visits Arnoux’s china factory and is shown around by Madame Arnoux. Frédéric makes an advance, which Madame Arnoux rebuffs.
Frédéric begins pursuing Rosanette in earnest and takes her to the races, but she goes home with a man named Cisy. At dinner one night at Cisy’s opulent home, Cisy reveals that he had gone home with Rosanette to win a bet. The guests talk about Arnoux and lewdly suggest that Madame Arnoux has been a mistress to many men. Frédéric throws a plate at Cisy, and the argument escalates. The men agree to a duel, but on the appointed day, Cisy faints.
Frédéric returns to Nogent to visit Roque’s daughter, Louise, whom he is considering marrying.
Deslauriers decides to pursue the potential job with Dambreuse as well as Madame Arnoux, but he is unsuccessful. He tells Madame Arnoux that Frédéric is getting married.
Frédéric returns to Paris to think. He wants to marry Louise because of Roque’s wealth but believes this would prove his weakness. He goes to Arnoux’s factory to buy two statues for Louise. There, Madame Arnoux reveals her bitterness about his impending marriage and his affair with Rosanette, both of which Frédéric denies. He claims he loves her and they begin spending more time together, although not as lovers. Frédéric grows frustrated and tries to get Madame Arnoux to visit him in an apartment he has rented expressly for them. But her child, Eugene, grows ill, and she takes it as a sign to stop spending time with Frédéric. Frédéric takes Rosanette to the apartment instead, and they become lovers.
The monarchy of King Philippe is disintegrating, and the Republic has triumphed. Dambreuse suggests that Frédéric run for the National Assembly, but Frédéric’s brief attempt ends in failure.
Frédéric finds out that Arnoux is still Rosanette’s lover. He tries to get Rosanette to choose between them, but she refuses. Frédéric takes Rosanette out of Paris, where their relationship deepens. While there, he finds out that Dussardier has been wounded in the fighting in Paris, and he returns there to find him. Meanwhile, Roque has come to Paris to join the fighting, and Louise has come too, hoping to see Frédéric.
At a party at the Dambreuses’ house, which Roque and Louise attend, the guests discuss the state of the city. Louise is jealous when she sees Madame Dambreuse flirt with Frédéric, and Madame Arnoux warns her not to trust him. Later, Frédéric tells Louise he cannot marry her.
Frédéric and Rosanette settle into a cozy domestic life. However, when he finds out that Arnoux and Madame Arnoux are nearly estranged, he visits Madame Arnoux, and they kiss. Rosanette, who has followed him, sees this. At home, he is so angry he nearly hits her, but Rosanette reveals that she is pregnant. Frédéric decides to make Madame Dambreuse his mistress, and she gives in. He is glad to be deceiving Rosanette.
Deslauriers begins working for Dambreuse, and he is in touch with Roque. Dambreuse dies, and Madame Dambreuse asks Frédéric to marry her. He agrees, then finds out Dambreuse has left nothing to Madame Dambreuse. Rosanette gives birth to a son, and Frédéric secretly splits his time between the two women.
Rosanette is unable to pay off some debts she owes, and when she tries to cash in some shares Arnoux gave her, it turns out they are worthless. She takes him to court but loses, although Deslauriers assures her that she can win on a different charge.
Deslauriers goes to Nogent and spends the summer with Roque. He wants to win over Louise, and he tells the Roques and Madame Moreau that Frédéric is going to marry Madame Dambreuse.
Rosanette eventually wins her suit against Arnoux. But when Frédéric goes to congratulate her, he finds that the baby has just died. Pellerin paints a portrait of the dead child and tells Frédéric that Arnoux is leaving Paris with his family because they are so poor, thanks in part to Rosanette’s lawsuit, unless they can find twelve thousand francs. Frédéric tricks Madame Dambreuse into giving him the money, but it is too late. The Arnouxes have left. Madame Dambreuse finds out why Frédéric wanted the money and vows revenge. Deslauriers, still angry that Madame Arnoux rebuffed his advances, also wants revenge, and he advises Madame Dambreuse to sell some debts Arnoux owes her at auction. All the Arnouxes’ furniture and possessions will be sold.
Madame Dambreuse tricks Frédéric into attending the auction, and she buys something. Frédéric leaves her. He goes to Nogent, thinking he will marry Louise, but Deslauriers has already married her. Back in Paris, he sees Dussardier get killed by a policeman, who turns out to be his friend Senecal.
Several years go by. One day, Madame Arnoux surprises him at home. They renew their love for each other. But when she takes off her hat, Frédéric sees that her hair is all white. She has come to give herself to him, but he is uninterested. She leaves.
Frédéric and Deslauriers reminisce about the past. They decide that their best memory is when they tried to sneak into a brothel when they were much younger.