The play is set at the close of the Civil War in New England at the imposing Mannon estate. General Ezra Mannon is due back home soon, as is his son Orin, who fought in the Union army. Ezra’s beautiful wife, Christine, is having an affair with a clipper ship captain, Adam Brant. At the beginning of the play Ezra and Christine’s daughter Lavinia, a thin and cold young woman, talks with the family gardener, Seth, and realizes that Brant has been coming around the house not to court her but to see her mother. She also realizes that Brant is the child of David Mannon, Ezra’s father Abe’s brother. David had an affair with Marie Brantome, Abe’s French nurse, and, as a result, was exiled from the family. It seems that their child is now seeking revenge. Lavinia confronts Brant and he angrily confirms her suspicions. Later Lavinia confronts her mother and warns her that she must desist from her adulterous relationship. Christine, who has no love for her daughter, nevertheless lies and promises to do so. When she sees Adam again she convinces him that they must poison Ezra; they can do this because Ezra has heart trouble and they can replace his medicine with poison.
A week later Ezra returns home from the war. Lavinia is elated, having an intense and passionate love for her father. Ezra is pleased to see Christine and tells her he wants to break down the wall between them. They retire to their bedroom, which distresses Lavinia. After their lovemaking, Christine steals away but Ezra is awake and accuses her of wanting to get away from him. They quarrel and Christine reveals the truth about Brant. Ezra’s heart begins to act up and Christine slips him the poison. As he is dying, Lavinia rushes in. Ezra manages to say that it is not medicine and that Christine is guilty. After he expires Lavinia is shocked and devastated. Without Christine noticing, Lavinia finds the box of poison.
Orin arrives home from the war. He is accompanied by Peter, a neighbor who is in love with Lavinia (Peter’s sister Hazel is in love with Orin), and Lavinia. Lavinia warns Orin to be careful of Christine and not let her manipulate him. He is confused, but he is thrilled to see his mother. Mother and son embrace, and the unsettling closeness of their relationship is apparent. Orin asks her about this Brant fellow and Christine lies, saying he was courting Lavinia. Orin tells her how much he missed her and how he used to dream of sailing away to the South Sea Islands with her.
When Orin and Lavinia are alone again, Lavinia tells him about Brant and Christine’s affair. Orin is furious but loath to believe his sister. He agrees, though, to follow Christine and see if she goes to Brant.
The night after Ezra’s funeral Brant walks aboard the deck of his ship. He converses with a Chantyman and feels a chill of foreboding as to his own fate. Christine surprises him and tells him Lavinia seems to know about the murder and that they must go away. Brant agrees, and the two plan to sail to China as soon as possible. Christine departs.
While Christine and Brant were talking, Lavinia and Orin had hidden themselves and listened to their mother’s conversation. After her departure, Orin shoots and kills Brant. He and Lavinia make it look like a robbery.
Back at the house, Christine is nervous about Brant, and seeks comfort from the sweet and innocent Hazel. When Orin and Lavinia return, they tell their mother about Brant’s death. Christine is undone, and even though Orin tries to tell her that the two of them can be happy now, she goes inside and shoots herself. Lavinia believes it justice, but Orin is tortured by what he sees as his role in her death.
A year later, Seth, Peter, and Hazel discuss the imminent return of Orin and Lavinia, who had traveled to China. When the brother and sister arrive, Orin looks haggard and old but Lavinia now looks beautiful and sensuous like her mother. Peter marvels at her changed appearance and disposition, and she tells him excitedly that they can marry and have happiness now. Orin, though, needles Lavinia about how much she liked the South Sea Islands that they visited and how she cavorted with the natives. Lavinia is angry with her brother but tries to help him leave the past behind.
A month later, though, it is clear that Orin is still bitter and guilt-ridden. He tells Lavinia he wrote a manuscript detailing all the Mannon crimes, and that a large portion of it is about her. She is furious but he accuses her of untoward behavior with a native, Avahanni. When she admits she engaged in lust with him, Orin attacks her.
Meanwhile, Hazel and Peter are growing concerned with Orin and Lavinia, respectively. Hazel wonders why Lavinia seems to control Orin so much. Peter dismisses her concerns and departs.
Orin rushes to Hazel and thrusts the manuscript in her hands, warning her that if Lavinia goes through with marrying Peter, Peter must read this. Hazel agrees. Lavinia sees the two of them and notices the manuscript. She tells Orin she will do anything if he surrenders it. Orin gives pause, and grimly tells Hazel it is over between them. He sends her away, confused and upset.
Orin turns to Lavinia and tells her that she must know what he wants, insinuating that the two of them will have a sexual relationship. Lavinia cannot believe this and cries out that he is insane. He insists it is the only way to stay together. Lavinia bursts out that she wishes he was dead, which makes Orin realize this would be just. He goes into his study, telling the newly returned Peter that he is simply going to clean his pistol. In the other room, he shoots himself dead.
A few days later Lavinia appears like her old self—dour, dark, and grim. Hazel confronts her and tells her to leave Peter alone, as she has influenced him and made him crueler. When Peter joins Lavinia she frantically tries to hold onto their love, even proposing a quick marriage. Peter is suspicious, and Lavinia clings him and accidentally calls him “Adam.” Peter cannot understand and asks about the native man. Lavinia suddenly realizes her fate is neither love nor happiness, but rather to live out her days closed up in the Mannon house. She orders Peter away and tells Seth to board up the house. There she will be with the Mannon ancestors and see the curse to its end. She goes inside and shuts the door behind her.
