It is later in the afternoon, and Gina and Hedvig wonder where Hialmar is. Dinner is late, a feature unusual in the Ekdal home. Finally Hialmar arrives, looking tired and worn. They think he is ill because he refuses to eat. He increases their anxiety by announcing that from now on he shall begin to take all the work in his own hands. What about the invention, asks Gina. Hedvig implores, "And think about the wild duck, father, and all the hens and rabbits." He will never set foot in that garret again, Hialmar says; "I should almost like to wring that cursed wild duck's neck!" Hedvig covers her ears. "Oh no, father, you know it's my wild duck," she cries and shakes him. For her sake, Hialmar promises, he shall never harm the bird. After Hedvig goes for her afternoon walk, the husband and wife are able to talk.
Questioning Gina, Hialmar forces her to admit of her previous liaison with old Werle. She was afraid to tell him before their marriage, Gina says, for fear he would change his mind. Now that their home is cozy and happy, more money comes in every day, they can forget about past happenings, she tells him. "This dull callous contentment," rails Hialmar; our home is mired in "the swamp of deceit." While Gina cries, Hialmar morosely observes that his "whole dream has vanished."
Beaming with satisfaction, Gregers confidently enters. Where he expected "the light of transfiguration" to shine from husband and wife, he is surprised to find nothing but "dullness, oppression, and gloom," he says. He cannot understand why Hialmar, with his sensitive perceptiveness, is unable to "feel a new consecration after the great crisis." Relling enters at this point, rudely asking Gregers his purpose in coming here. "To lay the foundations of a true marriage," responds young Werle. The physician reminds them that, although they are free to mess up their lives, they must remember a child is involved. Hedvig is at a critical age, he says, where she has "all sorts of mischief in her head." Hialmar promptly vows he shall protect his child "so long as I am above ground."
At this moment Mrs. Sorby pays them an unexpected visit. About to leave for the Hoidal works where she and Werle are to be married, she wishes to say good-bye. Having been a friend of Mrs. Sorby for many years, Dr. Relling announces that he shall mourn his loss during a drinking binge with Molvik this night. Gregers threatens to let his father know of Mrs. Sorby's previous connection with Relling. He knows everything that can be truthfully said about me, answers the housekeeper, nor does he keep any secrets from me. Moreover, she tells Gregers, this marriage is not entirely one-sided; now that your father is going blind he needs someone like me "to stand beside him and care for him." Hialmar is startled. "Going blind?" he says wonderingly. "That's strange. He too going blind." Taking affectionate leave of Gina, Mrs. Sorby exits.
When Hedvig comes in, she shows her father a letter which Mrs. Sorby gave her as a birthday present. Written in Werle's hand, the letter grants a monthly allowance of one hundred crowns to Lieutenant Ekdal, which will, upon the old man's death, continue as a lifelong settlement upon Hedvig. Hilamar draws the shocking conclusion, and sends Hedvig out of the room. He turns to his wife, asking whether or not the child is really his daughter. Gina pleads ignorance and admits she does not know. "Gregers, I have no child!" wails Hialmar, while Hedvig rushes in and embraces her tearful father. He shrinks from her touch. "Keep far away. I cannot bear to see you," he cries. "Oh! Those eyes!" And Hialmar plunges out of the house. Gina tries to comfort her sobbing daughter. Going out to fetch Ekdal, she leaves Gregers and Hedvig alone onstage.
Young Werle suggests that Hedvig sacrifice the wild duck to show her love for her father. This free will offering of "the dearest treasure you have in the world" will provide Hialmar proof of Hedvig's devotion. The child is hopeful and says she will ask her grandfather to shoot the bird for her. Gina comes back, saying that Ekdal had gone out with Relling and Molvik. Gregers wonders that he should go out "this evening, when his mind so sorely needs to wrestle in solitude." The curtain falls as Gina tries to comfort the sobbing Hedvig.
In this act, Gregers believes his mission is accomplished. Having disclosed the truth about Hialmar's family, the young Werle looks forward to viewing the process of purification in his friend. The outcome, however, is ironic: In a fit of self-indulgent martyrdom Hialmar rejects his family. Though he has said he will protect his child until he is buried, the father renounces Hedvig as soon as he discovers she is old Werle's daughter. Escaping from the inner conflict this knowledge has aroused, Hialmar goes off on a drinking binge with Relling and Volvik.
Gregers, however, still believes that his friend is capable of laying the foundations of a new life. He now carries his "claim of the ideal" to Hedvig. Gregers believes that if she would show her love by sacrificing the wild duck, Ekdal will recognize the value of his family ties. He furthermore thinks that once the wild duck is destroyed, the Ekdal household will be freed from the curse of delusion and fantasy. By this train of thought Gregers unwittingly commits the same logical error he tries to make Hialmar avoid: He acts on the belief that if the symbol of fantasy is effaced, then the Ekdals' lives will be devoted to a truthful acceptance of their lot.