Figures from the past convene on Mrs. Alving's house. Oswald has come home; Pastor Manders is on a visit; Engstrand is working on the house, and Regina is preparing for the Memorial. Mrs. Alving is satisfied because everything's going according to plan. By tomorrow, the threat of her husband's memory will be gone.
This action introduces a new threat to the control Mrs. Alving has established over the house. She is forced to change her game plan and even considers telling the truth about Captain Alving's life.
Mrs. Alving comes to understand that Oswald is seriously ill with the same disease that afflicted her husband. Listening to Oswald's description of the spiritual freedom and health he experienced in Paris, and the fear of misery he feels at home, Mrs. Alving understands her husband in a new light and vows to tell her son (and Regina) the truth. The fire at the Orphanage interrupts her.
Urged on by the destruction of her monument to deceit, Mrs. Alving lays it on Oswald and Regina. The goal she pursued throughout the play – burying her husband – has been transformed into a need to exonerate him.
Regina leaves the house, and with her Oswald's last chance to spare his mother a horrible request. His health is disintegrating and he wants her to put him to death. She agrees, but doesn't believe the end will come soon.
In a long speech, Mrs. Alving calls Oswald's attention to the sun breaking over the fjord. She promises to give him everything he wants, and continues to treat him like a little boy.
Oswald has urged his mother to detach herself from him, but she hasn't been listening. Now she's faced with the choice of killing him as he's requested and giving up her last ghost, or nursing him.