In June 1933, one week after Commencement, Kay Leiland Strong becomes the first of her Vassar College class to marry. Her groom is Harald Petersen, an aspiring playwright. The wedding at St. George's Church in New York is attended by seven young women who form Kay's close-knit college "group": Elinor "Lakey" Eastlake, Dottie Renfrew, Polly Andrews, Helena Davison, "Pokey" Prothero, Libby MacAusland, and Priss Hartshorn. Each has post-graduation plans reflecting the progressive ideals of their Vassar education. The ceremony is awkward: Kay has no family present, the curate rushes through the service, and Lakey, who privately considers the affair a humiliation, disappears before the reception. At the breakfast afterward, Dottie meets Dick Brown, a handsome, bitter painter and neighbor of Harald's.
Two nights later, Dottie goes to Dick's furnished room and loses her virginity. Dick is methodical and detached; Dottie experiences an unexpected orgasm, which surprises both of them. The next morning, he tells her to get fitted for a diaphragm, which Dottie interprets as a promise of continuing involvement, but Dick warns her bluntly that he does not love her. Three days later, Dottie visits a birth-control doctor and is successfully fitted. When she calls Dick afterward, he is not home. She sits on a park bench in Washington Square for nearly six hours, calling repeatedly. As night falls, she slips the contraceptive equipment under the bench, flees to the Vassar Club, a New York residence for alumnae, and catches the early train to Boston, never to see Dick again.
That September, Harald loses his job after openly criticizing his director. Kay works at Macy's in the management training program while the couple quarrels over money. Kay discovers an unfinished letter Harald wrote to his father before their wedding, admitting he does not know whether he loves her and describing their marriage as "a pledge to the future."
By Washington's Birthday 1934, Harald has sold an option on his play to a producer, and the couple throws a party. Updates on the group emerge: Dottie has returned from Arizona engaged to Brook Latham, a wealthy widower; Priss is pregnant. Helena goes to the kitchen and discovers Harald and Norine Schmittlapp Blake, a Vassar classmate, locked in a passionate embrace. She says nothing. Later, Harald mocks a cake their maid brought, seizes his manuscript, and throws it down the incinerator. Kay calmly reveals that copies exist, exposing the gesture as hollow.
The next morning, Norine confesses to Helena that she and Harald have been lovers. She explains through elaborate psychological reasoning that Harald became a "male potency symbol" because her husband Putnam is impotent. Helena loses her temper, telling Norine to stop seeing Harald. A week later, newspapers report that Harald and Putnam have been arrested for leading a sympathy walkout in support of striking hotel waiters, with Norine photographed in a tiara and evening gown.
In Boston, Dottie's mother mentions the arrest story during a day of wedding errands. Dottie becomes agitated, hoping the second man arrested might be Dick Brown. When she discovers it is Putnam Blake, her suppressed feelings overwhelm her. She confesses to her mother that she is still in love with Dick. Mrs. Renfrew proposes postponing the wedding, but Dottie refuses, insisting she has made up her mind to marry Brook.
Meanwhile, Libby MacAusland struggles in publishing and is fired by her editor, Gus LeRoy, for lacking practical judgment; she moves to literary agenting. At a party Libby hosts, Polly Andrews meets Gus, and they begin a love affair lasting nearly a year. Gus is in psychoanalysis, which his estranged wife Esther initiated as a condition for considering divorce; the analyst's rule against changing one's life during treatment prevents Gus from leaving his marriage. One evening, Gus tells Polly he must stop seeing her. Polly tells him she believes he will return to his wife. Under her door, she finds a letter from her father, Henry Andrews, announcing his divorce and asking to live with her.
In a parallel narrative, Priss Hartshorn Crockett nurses her newborn son Stephen under her husband Sloan's rigid insistence on breast-feeding. Priss endures painful sessions and sleepless nights. Her obstetrician, Dr. Turner, quietly overrules Sloan's opposition to a supplementary bottle. Priss privately recognizes the enterprise as "completely unnatural, strained, and false."
Mr. Andrews arrives and moves into Polly's building, but his generous spending strains their finances. Polly borrows from the Morris Plan, a small-loan lender, and begins selling her blood at the hospital. Dr. Jim Ridgeley, a young psychiatrist she consulted about her father's manic episodes, catches her giving blood, declares he is falling in love with her, and proposes. Polly agrees, won over by his goodness, though she is not certain she loves him. They elope.
In March 1938, Polly arrives at the Payne Whitney Clinic, the psychiatric facility attached to New York Hospital, to give a routine test and discovers the patient is Kay, who has a black eye and bruises. Kay recounts that Harald came home drunk, beat her when she accused him of infidelity, and locked her in the dressing room. When police arrived, Harald convinced them they were rehearsing a play. Afterward, Norine persuaded Kay she needed hospital rest, and Harald signed commitment papers placing Kay in the psychiatric ward without her knowledge. She did not realize where she was until nurses took her belt and matches and tried to remove her wedding ring. Jim Ridgeley tells Kay her hospitalization is "a crime" and gets her moved to the convalescent floor. Harald appears that evening, confesses to the psychiatrist, and Kay is told she may leave. She chooses to stay for medical checkups, but Harald then suggests she remain for psychiatric treatment and have Norine speak to the doctors. Kay panics and begs him to keep Norine away, left doubting whether her choice to stay is truly her own.
In June 1939, Priss encounters Norine, now remarried to Freddy Rogers, a wealthy banker, in Central Park. Norine has adopted a permissive child-rearing philosophy that horrifies Priss. Norine confides that she was "madly in love with Harald" for four years and that he would periodically revisit former lovers to confirm their availability.
In July 1940, Kay is dead at 29, having fallen from the twentieth floor of the Vassar Club while airplane-spotting. The police rule it an accident; Helena's mother, Mrs. Davison, the last to see Kay alive, testifies that Kay was in excellent spirits, discussing Churchill, the air raids, and a job interview. The group arranges an Episcopal funeral at St. George's Church, the same church where Kay married seven years earlier. They lay her out in a Fortuny silk gown that Lakey purchases, a dress Kay had always longed for. Lakey has returned from Europe with her companion, the Baroness d'Estienne, revealing that she is a lesbian. At the funeral, Harald enters last and kneels conspicuously at the back.
After the service, Harald asks to ride with Lakey to the cemetery. In her car, he insists Kay killed herself deliberately, driven by competitiveness with his own faked suicide attempts. He claims he never loved Kay or any woman, suggests he and Lakey are the "two superior people" in the group, and presses Lakey about whether she had a sexual relationship with Kay. Lakey refuses to confirm or deny, allowing Harald to torment himself with uncertainty. He demands to be let out of the car. Lakey stops, and he gets out, attempting to hitchhike back to New York as the funeral cortege passes him.