On Grand Isle, a summer retreat for wealthy French Creoles from New Orleans, Léonce Pontellier, a forty-year-old businessman, tries to read the newspaper despite the noise around him, scolds his wife, Edna, for going to the beach during the hottest hours, and then leaves to play billiards.
Edna and Robert Lebrun, a son of the guesthouse's owner, talk about his plans to seek fortune in Mexico, her childhood in Kentucky, and her sister Janet's upcoming wedding.
Léonce returns late that night, wakes Edna to talk, checks on their sons, and asks her to check one of them, who seems feverish. Edna, wide awake and unhappy, weeps on the porch. The next morning, Léonce goes back to New Orleans for business and sends Edna bonbons from there.
Léonce thinks about his dissatisfaction with Edna's treatment of him and their sons, as she doesn't idolize or worship them. Back on Grand Isle, Edna, Robert, and her friend Adèle Ratignolle eat the bonbons and talk about sewing, chocolates, and childbirth.
Robert tells Edna about his plans to be her attendant this summer, as he was of Adèle in the past. Edna draws Adèle, but dissatisfied, throws the drawing away. After Adèle experiences a fainting spell and retires to her cottage, Robert convinces Edna to go for a swim.
Edna feels seduced by the sea and begins to realize her relations to the world within and around her.
Edna becomes less reserved with Adèle and tells her that, this summer, she feels as if she's walking through a meadow idly, unguided as she did once in her youth. She concludes her relationships with men had been more intense than those with women; that she had married Léonce to end her unrealistic love fantasies; and that she doesn't feel fit for motherhood responsibilities.
Concerned that Edna will take Robert's attentions seriously and ruin her reputation, Adèle warns him to let Edna alone.
At a Saturday-night celebration a few weeks later, when Mademoiselle Reisz plays the piano, Edna is overtaken by emotions. Robert suggests everyone goes for a nighttime swim.
After the party, Edna swims into the sea alone for the first time and feels emotional about it. Robert follows her home, tells her a story to show he understands her feelings, and stays with her on the porch until Léonce returns.
After Edna, who has collapsed in the porch hammock, refuses to go to bed, Léonce stays with her outside until dawn.
Next morning, Edna and Robert go across the bay for Sunday mass. On the boat, Robert talks to a flirtatious Spanish girl, Mariequita. Then he proposes exploring other places with Edna in the next days, and she entertains the idea of being alone on the islands with him.
During mass, Edna feels oppressed and drowsy, so Robert takes her to rest at a cottage. When she awakens, she joins Robert at the garden, jokes they are the only remaining members of their race, and then spends the afternoon there with him and later with the cottage's owner.
When they return home, Robert and Edna put her son Etienne to bed, then he leaves, and she waits for Léonce, who had gone to the club for business after hearing Edna was fine.
One day at dinner, Edna is shocked to hear that Robert is leaving for Mexico that evening. When he comes to say goodbye, she recognizes her infatuation for him.
Missing Robert, Edna visits Madame Lebrun to see his pictures and read his letters, questions Léonce after he sees Robert in New Orleans, and talks about him with Mademoiselle Reisz, who gives Edna her address in New Orleans and urges her to visit.
Back in New Orleans, Léonce, worried about his business relations, scolds Edna one evening for not staying home to receive visitors, as she usually does on Tuesdays. He complains about the meal and leaves to the club for dinner. Edna, after trying to crush her wedding ring unsuccessfully, shatters a vase.
The next morning, Edna declines Léonce's request to meet him in town and, instead, visits Adèle, staying for dinner and then pitying the Ratignolles' domestic harmony.
Displeased by Edna's refusal to submit to his demands and her dedication to painting, Léonce scolds her for neglecting their family, urges her to follow Adèle's example, and speculates if she suffers from mental problems, as her mood fluctuates wildly.
Edna visits Madame Lebrun to ask for Mademoiselle Reisz's new address and hears the contents of Robert's letters from Victor, who later comments to her mother that Edna doesn't seem like the same woman.
Edna visits Mademoiselle Reisz, who tells her an artist must have a courageous soul, hands her a letter from Robert mostly about her, and plays her a Chopin Impromptu, per Robert's request.
Léonce expresses his concerns about Edna to Doctor Mandelet, his friend and family physician, who advises him to let her do as she likes and promises to come for dinner to check on Edna, who he suspects might have another man.
Edna's father, a former Confederate colonel, comes to New Orleans to go shopping for her sister's wedding. Edna sketches her father and takes him to the racetrack and to Adèle's soirée musicale. Doctor Mandelet comes to dinner and tells a story about a female patient who pursued stray affections. Edna responds with a story of a woman who disappears with her lover, and the doctor confirms his suspicions about her.
Edna argues with her father over her refusal to attend Janet's wedding, so Léonce decides to attend it alone on his way to New York for a long business trip. Their children also leave for her mother-in-law's country home. Once alone, Edna is overtaken with a radiant peace.
While her family is away, Edna goes to the races with Alcée Arobin, an infamous seducer, and Mrs. Highcamp. She goes again only with Alcée and has dinner with him. After he kisses her hand, she feels nervous as if she had betrayed Robert.
Alcée continues to flirt with Edna, which gradually pleases her. She visits Mademoiselle Reisz and reveals her plans to rent a small house around the corner. She reads Robert's latest letter, learns he will be returning soon, confesses her love for him, returns home excited, and writes to Léonce about her intention to move for a while into the small house.
Alcée visits Edna that evening, kisses her, and she responds.
After Alcée leaves, Edna cries, regrets the kiss was not motivated by love, feels her love for Robert growing and feels that she finally understands the meaning of life.
Without waiting for Léonce's reply, Edna prepares to move to the small house. Alcée visits and reminds her of the dinner celebration she had planned, and he begs to see her sooner, but she scolds him, laughing.
Edna hosts a small celebration of her new home and announces it is her twenty-ninth birthday. Victor sings a song Robert used to sing for Edna, and she makes him stop, bringing the night to a close.
After the party, Alcée helps Edna shut up the big house, accompanies her to the small one, which he has filled with flowers, and caresses and kisses her.
Léonce writes disapproving of Edna's move and, to save appearances, arranges for their home to be remodeled, and advertises in a newspaper that they are taking a vacation abroad. Edna enjoys a visit to her children at their grandmother's home.
Adèle visits Edna and warns her about Alcée and her reputation. Edna visits Mademoiselle Reisz and discovers that Robert is back. He walks her home, questions her about a photo of Alcée, and agrees to have dinner with her.
Edna and Robert become ceremonious during dinner, and she jealously questions him about a Mexican girl who gave him a tobacco pouch. When Alcée drops by, Robert leaves. Edna sends Alcée away and can't stop thinking about her distant encounter with Robert.
The next morning, hoping to see Robert again, Edna responds to letters from her son Raoul and from Léonce, but not to a note from Alcée. As Robert doesn't visit her again, one night she goes out with Alcée to the lake, returns home with him, and loses her hopes about Robert.
Edna runs into Robert in a garden café and dines with him. She expresses her disappointment at his indifference, and he accuses her of cruelty. They go to her house, kiss, confess their love for each other, and discuss their fantasies about being together. Edna leaves to be with Adéle, who is in labor, but asks Robert to wait for her.
After watching in agony as Adéle gives birth, Edna kisses her goodbye, and Adèle tells her to think of the children.
Doctor Mandelet accompanies Edna home, learns that she doesn't intend to travel with Léonce, comments about sexual passions, and offers to be her confidant if she needs help. She discovers that Robert has gone but left her a note saying goodbye because he loves her. She lies awake all night.
Edna goes to Grand Isle, sees Victor and Mariequita, and walks to the beach. After observing a bird with a broken wing crashing into the surf, she removes her old bathing suit and feels like a new-born creature. She swims out thinking of Léonce, her children, Robert, and Mademoiselle Reisz's words about the courageous soul an artist must have. Eventually, she swims far from the shore, exhaustion overtakes her, and memories of her childhood fill her thoughts.