Hialmar asks hesitantly if anyone has found his hat on the stairs; apparently he lost it the night before. Gina chastises him and enters the kitchen to fetch a breakfast tray for him. While she is out, Hialmar hastily examines the torn letter from yesterday. He refuses food upon her return. When Hedvig enters the studio again, he rejects her anew and storms into the next room and Gina follows. Terrified, Hedvig takes the pistol from the shelf and creeps into the garret.
Hialmar and Gina argue over packing. Utterly exhausted, Hialmar slumps onto the sofa and unthinkingly begins to eat his breakfast. In face of the endless preparations involved in the prospective move, Gina suggests that he stay in the sitting room for a few days. Hialmar ultimately agrees. He also glues Werle's letter back together. After all, it is for his father, and not he, to decline Werle's offer.
Gregers enters and Hialmar quickly rises. Gregers attempts to strengthen Hialmar's resolve to adhere to the ideal. Hialmar has his invention before him and reveals that it invention was Relling's idea. It brought him happiness only in inspiring Hedvig's faith. Now he is convinced Hedvig has been false with him. She has never truly loved him and would readily run off with the Werles if promised their fortune. Hedvig "[blots] the sunlight" from his life.
Suddenly a shot rings out from the garret. Gregers is triumphant: he announces that Hedvig has gotten her grandfather to sacrifice her precious duck to prove her love for her father. Suddenly Ekdal appears in full uniform. The group realizes that he has not shot the duck—it would appear Hedvig has done it herself.
Hialmar tears open the garret door. The group follows, only to discover Hedwig lying on the floor. The men lay her on the couch as Gina calls for Relling. Ekdal murmurs quietly that the woods have avenged themselves. Upon examining her, Relling declares the child dead; the bullet has pierced her chest and caused an internal hemorrhage. "In the depths of the sea" murmurs Gregers. Hialmar screams remorsefully that he hunted her from him like an animal. Molvik makes a drunken benediction. Gina asks that they take her to her room. She and Hialmar must help each other mourn. Now Hedvig belongs to both of them.
Once the members of the household have left, Relling informs Gregers that Hedvig certainly killed herself. Gregers consoles himself that Hedvig did not die in vain but set free "what is noble" in her father. Relling retorts that this nobility will not last—within a year Hedvig will be but a "pretty theme for declamation." Moreover Gregers has little reason to concern himself with the Ekdals further: people do fine if others do not pester them with talk of ideals. If Relling is right, Gregers declares, life is not worth living. Walking off, he announces that he is glad of his destiny—to be the thirteenth at the table. "The devil it is" answers Relling.