In the first act, Charles Marsden visits Professor Leeds in his New England home, where they discuss Leeds’ daughter, Nina, who is struggling after losing her love, Gordon, in the war. Nina is distant and rebellious toward her father, showing signs of emotional turmoil. She plans to leave, believing she must find herself and atone for her perceived failure with Gordon. Leeds is initially resistant but ultimately agrees to let her go. Nina confesses that she feels guilty for not sleeping with Gordon before his death and expresses a deep need to give of herself to others, particularly wounded soldiers. Marsden is repelled by her actions, while Leeds feels sorrowful to lose his daughter. Nina leaves, and Leeds reflects on his loneliness.
In the second act, a year has passed, and Marsden reflects on the professor's death. Nina has become a nurse but remains emotionally distant and cold. Marsden is perplexed by her lack of grief over her father's passing and is uncertain about his feelings for her. Nina is seen with a doctor, Ned Darrell, and Sam Evans, a young man who loves her. Evans confides in Marsden that he wants to marry Nina. Darrell expresses concern to Marsden about Nina’s emotional state, suggesting she is using her nursing to atone for her guilt. Marsden awkwardly agrees to help, though he remains conflicted.
Nina reveals her numbness and disillusionment with life, confessing that she has slept with several war veterans to punish herself. Marsden suggests she marry Evans and have children, and she agrees. The act ends with Nina seeming to find some comfort in Marsden's support.
Seven months after marrying Sam Evans, Nina is living with him and his mother in a lifeless home in upstate New York. Though the house feels soulless, Nina is calmer and more stable, and she reveals through a letter to Ned Darrell that she is pregnant and content. Marsden visits and guesses her condition, feeling bittersweet closure. Sam is happy but insecure, and his mother, troubled by Nina’s pregnancy, reveals a devastating family secret to Nina: mental illness runs in the Evanses' lineage. She implies Nina should terminate the pregnancy to prevent the curse from continuing. Nina is horrified, but as they talk, Mrs. Evans subtly suggests another solution—finding a healthy man to father a child in secret. Deeply shaken, Nina clings to the idea of personal happiness and rejects religious guilt.
Seven months later, Nina and Sam are back in her father’s old home, now emotionally frayed. Sam is defeated by work and marital tension, and Nina, thin and worn, is plagued by guilt and ambivalence after aborting her child. Their marriage is hollow, and Nina still obsesses over her longing for motherhood. Marsden arrives with edits on her biography of Gordon but is inwardly judgmental, particularly regarding Nina’s abortion, which he assumes Darrell performed.
When Darrell visits, he notices the strain in Nina’s marriage and is surprised when she confides in him about the family’s mental illness and her abortion. Desperate for purpose and redemption, Nina proposes the idea of conceiving a child with a man she does not love, so long as Sam never knows. Darrell, always having been physically attracted to her and desirous of experiencing happiness in his own life for once, agrees to be the man.
Nina, now pregnant again, feels triumphant and fulfilled by her love for Ned, though she hasn’t heard from him recently. Evans enters full of anxiety and guilt over his career failures, while she struggles between contempt and sympathy for him and still keeps her pregnancy secret. When Darrell arrives, bitterness turns to passion between him and Nina, though he insists their affair should remain emotionless. She demands love, and when he says impulsively that he loves her, she takes it as truth. Marsden then arrives, grieving his mother’s death and sensing tension among them. Darrell later tells Nina they must stop, reminding her that their arrangement was only for Sam’s sake, not love. But she insists her unborn child needs its father. They nearly reconcile before Evans returns.
Darrell tells Evans the truth about the baby but lets Sam believe it’s his; Sam is overjoyed, and Nina, shaken, decides to keep silent. Feeling the baby move, she realizes it belongs only to her.
A year later, Nina lives peacefully with Sam and their son, Gordon. Sam has become a confident, loving husband and father, while Marsden visits, aged and melancholic. Marsden mentions seeing Darrell in Munich with another woman, provoking Nina’s sharp reaction and confirming his suspicions of their past. After Evans leaves to attend to business, Darrell suddenly arrives, weary and nervous. Nina’s joy and dread intertwine as she greets him. Marsden subtly taunts them and then departs to find Sam, suspecting Darrell might be Gordon’s true father.
Alone, Nina and Darrell confess they still love each other. He pleads for her to leave with him and the baby, but she refuses—she cannot destroy Sam’s happiness. When she coldly offers to keep Darrell as her lover, he threatens to tell Sam the truth but falters when Sam enters, warm and welcoming. Nina, feeling strangely whole, gathers the three men—husband, lover, and father—around her. Each represents a part of her fulfillment, and she feels them merging within her. Pregnant again and radiant, she says goodnight to them all, content in her power and the strange unity she has created.
Eleven years later, Nina lives with Sam and their son, Gordon, in an elegant Park Avenue apartment. Though still beautiful, she is tense and weary. Darrell, now gray and aimless, visits often, much to Gordon’s annoyance. Nina feels trapped between love and resentment toward Darrell, who in turn feels bound to her and envious of Sam’s easy happiness. When Nina asks when he will return to the West Indies, Darrell admits he no longer works seriously and bitterly reflects on his past “experiments.” Their conversation turns painful as they acknowledge their loveless situation. Gordon, rude to Darrell, smashes the gift he receives from him after secretly seeing him kiss Nina. Darrell tries to calm him, urging him to keep silent, and the confused boy agrees. Sam arrives, oblivious and cheerful, and the family shares lunch. Gordon’s questions about his name and his parents’ past unsettle Nina, but she reassures him with a lie that restores his affection. Yet as he clings to her, she feels him slipping away emotionally toward Sam.
A decade later, aboard the Evans family yacht at Gordon’s rowing race, the years have aged everyone differently. Nina’s hair is white, her beauty forced; Darrell, tanned and rejuvenated; Marsden, old and grief-stricken; Sam, comfortable and stout; and young Madeline Arnold, fresh and lively, soon to marry Gordon. Nina is jealous of Madeline and mourns her fading youth and her lost closeness with her son. Darrell, detached, feels no enchantment with her anymore and talks dispassionately about his scientific work. Nina misreads this as bitterness and accuses him of replacing her with his colleague, Preston. She laments losing Gordon, feeling he has gradually become entirely Sam’s son.
When Madeline joyfully reports Gordon’s race progress, Nina’s jealousy deepens. She lashes out at Darrell, accusing him of forgetting her, and clings to him in a desperate attempt to revive their passion. He refuses to interfere further in her life. She suggests revealing the truth about Gordon’s parentage to Sam, but Darrell refuses. Marsden, drunk and self-pitying, enters and declares that he and Nina will soon marry and that he will finally write truthfully about life. In her delirium, Nina resolves to destroy Gordon’s engagement and tells Madeline the Evans family is cursed. Darrell intervenes, saying Nina is delusional and suffering from menopause, driving Madeline away. Crushed, Nina confides in Marsden that Sam’s family has hereditary insanity and that she conceived Gordon with Darrell to protect her child. Horrified but compassionate, Marsden forgives her and comforts her like a father.
As Gordon wins the race, Nina spirals into hysteria, crying that he belongs to her alone. Sam suddenly collapses from a stroke. Darrell tends to him and orders Nina to care for him faithfully. She agrees numbly, resigned to her duty. Marsden, sensing the end of all their struggles, feels grim satisfaction. The others turn toward Sam with guilt and love, while Madeline looks ahead to her future with Gordon, untouched by the older generation’s pain.
A few months after Sam’s death, the scene is set on the terrace of the Evanses' Long Island estate. Gordon and Madeline grieve, while Gordon, handsome and self-assured, expresses resentment toward Nina, partly blaming her for his father’s decline and speculating that she loved Darrell more than Sam. Madeline encourages understanding and compassion, urging him to accept that people cannot control whom they love.
Marsden appears rejuvenated and observes the young couple, feeling joy as his thoughts turn to Nina. Alone, Gordon reflects on his mother’s devotion to Sam despite her past love for Darrell, struggling to reconcile his feelings about her. Nina and Darrell then arrive, both visibly aged. Gordon remains distant and critical, prompting Darrell to reflect on how unaware Gordon is of the truths about his family and his mother’s past.
When Gordon reveals that Sam’s will left Darrell a half-million for research, Darrell initially wants to refuse, but Gordon insists. A brief altercation ensues when Gordon strikes Darrell to protect his mother, leading to a tense but clarifying exchange. Gordon admits he always suspected Nina and Darrell loved each other but ultimately accepts it, recognizing that Nina was a true wife to Sam and Darrell a true friend. He leaves, giving his blessing for Nina and Darrell’s past but signaling that the future belongs to others.
Darrell encourages Nina to turn her attention to Marsden for peace, and she agrees. Alone with Marsden, Nina confesses her love, and he happily embraces her, beginning to plan their life and wedding together. Darrell departs, reflecting on his dutiful role as a father to Gordon. Nina watches her son take off in his plane, realizing he has moved on, and likens his new life to the death of Gordon Shaw, the symbol of her past passions. Marsden comforts her, advising her to treat her life with the Gordons as a “strange interlude.” She accepts, at peace with leaving the past behind, calling him “Father” as they look forward to their shared future.
