Jakob Engstrand - A carpenter with a deformed leg, Jakob married Johanna when she was pregnant with Captain Alving's child. The daughter was Regina. At the start of the play, he is working on the orphan asylum meant to memorialize Captain Alving. He wants to use the money he is saving to open an "establishment" for sailors. When speaking to Pastor Manders, whom the hypocritical Jakob always tries to please, he describes the establishment as a place to reform sailors. But when he describes it to Regina, it sounds like a high-class saloon. He is an alcoholic.
After dinner, the Pastor and Mrs. Alving discuss this strange development. The Pastor realizes that Oswald is furious at Engstrand for never telling him the truth about Regina. Engstrand enters and suggests to the Pastor that he hold a prayer meeting at the orphanage. The Pastor questions him, and Engstrand convinces him that it was only to save Johanna's reputation that he kept the truth from him. Engstrand and the Pastor leave, and Mrs. Alving goes to talk to her son. Oswald is drinking. She wants to tell him the truth about his father. He tells her about the sickness he is suffering from. A doctor in Paris diagnosed it by saying that the sins of the father visit the son. He goes on to complain about the misery and hypocrisy of gloomy Norway, contrasting it with the joy of life. Mrs. Alving is about to tell him and Regina the truth, but then they notice that the orphanage has caught fire.
Engstrand and the Pastor return to the house, announcing that the orphanage is lost to the flames. Engstrand convinces the Pastor that there will be a public scandal, blaming the Pastor for carelessly letting the prayer candles start the fire. He blackmails the Pastor into funding his sailor establishment, convincing the Pastor that it will be dedicated to the reform of sailors. They leave, and Mrs. Alving finally tells Regina and Oswald the truth about their father. Regina feels cheated and goes to claim part of her inheritance. Oswald is partly relieved but reveals to his mother that he is sick beyond hope. He shows her some morphine pills and asks her to administer them in case of a relapse. As the sun comes up, he melts into his chair and begins to mumble nonsense. Mrs. Alving desperately searches for the pills, having seemingly lost all hope for her son or anyone else.