The play is set in late-19th-century Norway in the wealthy household of the Alvings. Jakob Engstrand, a ne'er-do-well carpenter, arrives at the garden room wanting to speak with Regina, his daughter, who works as a maid for the Alvings. She is not at all happy to see her father, whom she regards as dissolute and a drunk.
Engstrand has been working on the “Captain Alving Memorial,” an orphanage/asylum that is opening the next day. Now that this project is done, he tells Regina his plans to open a home for seamen, insinuating that it would be a brothel but a very good one. He suggests his daughter should come with him and work there, assuring her that she will be well off; she’s gotten too hoity-toity here at the Alvings’. Regina is disgusted and orders him away. She doesn’t want to leave and she doesn’t think it is appropriate to keep house for him. She also thinks he needs to leave because Pastor Manders will be here any minute. Engstrand consents to go, but he tells her to listen if the Pastor gives her any advice.
Pastor Manders greets Regina and they exchange pleasantries. He compliments her on how she’s grown up and suggests that she ought to go with her father. She insists that she wants a respectable position, and she asks him to keep her in mind if he hears anything. She fetches Mrs. Alving.
Manders greets the lady of the house. They discuss tomorrow’s opening of the orphanage, which was built with her late husband’s funds and intended to honor his memory. They also discuss Osvald, her son, who is upstairs resting now that he is home from Paris, where he works as an artist.
Manders is disturbed to find progressive and ungodly books in Mrs. Alving’s house, and she shrugs that she began looking for the truth due to the events of her early marriage. She did her duty and married Captain Alving, but he was a debauched man and she left him. She went to Manders for comfort; though the two of them loved each other, Manders did his duty and sent her back to her husband.
The conversation returns to the topic at hand, which is the memorial. Manders has been doing the business side of it and plans to give a speech at its opening tomorrow. He pressures Mrs. Alving not to insure the building since it would seem to demonstrate a lack of faith in Providence. Mrs. Alving agrees, though she thinks it’s a bit foolish since Engstrand accidentally started a small fire there the previous day. Manders defends Engstrand as trying to get his life together and says that Regina ought to go with him, but Mrs. Alving vociferously refuses to let Regina go.
Osvald comes downstairs. He is wan, handsome, and smoking a pipe. Mrs. Alving asks him to put it out and he acquiesces, saying he only wanted to try it because he has a memory of his father forcing him to smoke as a child until he threw up. Disconcerted, Mrs.Alving insists that his father was a perfect man. Indeed, that is how he was known in the town.
Manders finds Osvald’s stories of his time with fellow artists in Paris and his views on “the joy of life” and couples living together without getting married distasteful. After Osvald leaves, Manders excoriates Mrs. Alving for letting her son grow up like this, and he exhorts her to try to save him from his misguided views.
Mrs. Alving lets him lecture her, but when he concludes, she states firmly that she has to speak to him as well. She tells him frankly that everything he thinks about Captain Alving is false: her husband was never reformed and died just as dissolutely as he lived. He was charming and fooled people, but he did what he wanted. Once he seduced their maid—Regina’s mother—in their own home, she decided that enough was enough and she sent the woman, now with child, away. Regina’s mother revived an old relationship with Engstrand and Mrs. Alving gave her money to entice him. She had the baby, and later, Regina came to live in the Alving home.
Mrs. Alving rues that she endured so much and did everything she could to prevent the truth from coming out. She took care of Alving until he died, diverted all his money to the fund for the orphanage, and raised her own money for her and Osvald to live on. As soon as the memorial opens, she sighs, they will be free.
Manders is utterly stunned and says they will do their best to prevent scandal. Suddenly, the two of them hear Regina and Osvald together in the next room; Mrs. Alving gasps that it is the ghosts.
When the second act opens, Pastor Manders and Mrs. Alving discuss what to do. They agree Regina must be sent away, since Regina and Osvald cannot begin to carry on just as his father did. Mrs. Alving wishes there were an easy solution and would even seem to condone incest if they could just live happily and no one would know, but Manders rebukes her. Mrs. Alving speaks of how there are ghosts of the past everywhere.
Engstrand shows up, asking if Manders might give an evening prayer tonight at the memorial. Manders agrees, but he pressures Engstrand into admitting what he did in regard to marrying Regina’s mother. Manders is critical of him for being bought to marry a fallen woman, but Engstrand reframes this as him being a good Christian and helping a fallen woman. He promises that he did not take the money. Manders is convinced and apologies.
After Manders and Engstrand leave, Osvald approaches his mother and says he must tell her something. He explains that he is not tired from any ordinary illness: rather, his mind is broken and he cannot work. He went to a doctor who told him he’d been sick since birth with a hereditary illness. Osvald reacted poorly because he believed his father to be a great man, and he decided he must have contracted the disease because of the free way he lived in Paris. He bemoans the fact that he is ruined and getting worse, and he is full of a sense of dread. He tells his mother that he must go away and that Regina is his salvation.
All of this stuns and horrifies his mother, who begs him to stay with her and to not think of Regina that way. Pastor Manders enters the room just as Mrs. Alving is about to tell Osvald and Regina the truth, but they notice flames off in the distance and realize that the orphanage is burning.
In Act Three, the orphanage has completely burned down. Mrs. Alving is weary of the whole matter and tells Pastor Manders to settle it; she wants nothing more to do with it. He is dismayed about the whole matter, especially when Engstrand arrives and suggests that it is the Pastor’s fault and that everyone will disparage him. He insinuates that he would be willing to take the blame if the Pastor would help him finance the seamen’s home. The Pastor gratefully agrees, and both leave.
Osvald returns from the wreckage of the fire, fitful and upset. He claims that everything of Father’s memory will burn. Mrs. Alving finally tells him the truth that he has to stop blaming himself: it was his father who lived a terrible life and passed this disease onto him, and it was her fault for not making a better house for him. She also tells Regina the truth about who she is.
Regina immediately wants to leave. She is critical that she was not raised as a gentleman’s daughter and that she wants no more of them. Mrs. Alving sadly says that she will come to ruin. Regina leaves in a huff, saying that the Pastor will take care of her, or else she has a home—her father’s brothel—where she will do just fine.
Mrs. Alving promises to take care of Osvald and to be calm and patient with him. He asks if she would really do anything for him; when she answers "Of course," he explains that he’s already had one breakdown and is due for another. When this happens, he will be completely vegetative, like a child again. This repulses him, so he has gathered morphine pills. He hoped that Regina would take care of this if it came to it, but now the only one on whom he can rely is his mother.
Mrs. Alving cannot fathom this at all, but she shakily agrees, thinking it will never be possible.
After days of unceasing rain, the sun is beginning to come up. Osvald asks to see the sun, but something has happened and his tone is dull and lifeless. To her horror, Mrs. Alving realizes that his mind is gone. She clutches the pills, wondering what to do.
