The narrative centers on Mrs. Helen Alving on the eve of dedicating an orphanage built to honor her late husband, Chamberlain Alving. Pastor Manders arrives to manage the legal formalities, prompting a series of intense confrontations regarding duty, marriage, and societal convention. Mrs. Alving reveals to the pastor that her husband lived a thoroughly dissolute life until his death, and that she maintained a facade of a respectable marriage solely to protect her son, Oswald, from the truth.
Oswald returns home from Paris as an established painter, bringing with him modern ideas about art, freedom, and living arrangements that deeply shock Pastor Manders. Beneath his outward success, however, Oswald hides a terrifying medical reality. He reveals to his mother that his physical and mental faculties are breaking down due to an inherited disease stemming from his father's past excesses, leaving him crippled by a consuming dread of a living death.
Complications deepen when Oswald is drawn to Regina Engstrand, the household maid, who possesses the vitality and joy of life he feels he desperately needs. It is subsequently revealed that Regina is actually the illegitimate daughter of the late Captain Alving and the former maid Johanna, making her Oswald's half-sister. This disclosure shatters the remaining illusions of the household.
As tensions rise, the orphanage built to cement the family's honorable legacy burns to the ground uninsured, orchestrated through a web of deceit involving Regina's foster father, Jacob Engstrand. Amidst the ashes of the institution, Pastor Manders departs, anxious to protect his own reputation from scandal, while Regina abandons the estate to pursue her own future in the town.
Left alone with her son, Mrs. Alving faces the final crisis as Oswald's condition rapidly deteriorates into a complete mental collapse. Having previously extracted a promise from his mother to end his suffering should he become permanently incapacitated, Oswald begs her for assistance as the morning sun rises over the snow-peaks, leaving Mrs. Alving confronting the ultimate moral dilemma.
