It is Christmas in the comfortable Helmer home, and Nora returns laden with parcels. Her husband Torvald, newly promoted to manager of the bank, teases her about overspending and addresses her throughout as his little skylark, his squirrel, his songbird. The affection is real but it is the affection one shows a charming pet, and Nora plays the part, hiding a bag of macaroons and coaxing housekeeping money out of him with practiced sweetness.
An old friend, Mrs Linde, arrives looking for work, and to her Nora confides a secret she has guarded for years. Early in the marriage, when Torvald fell dangerously ill and needed a costly journey south, Nora found the money herself rather than from her father as everyone believes. She borrowed it from Krogstad, a lawyer at the bank, and has been quietly repaying it ever since out of her own scrimping, proud to have saved her husband's life without his ever knowing.
The secret turns dangerous when Krogstad, about to lose his post at the bank, threatens to expose her. To get the loan Nora had signed her dying father's name to the bond, and the date shows the signature was made days after his death. Krogstad, himself disgraced by a similar forgery, tells her plainly that the law judges the deed and not the motive, and that if he falls he will drag her down with him. Nora dances a wild tarantella to distract Torvald from the letterbox where Krogstad's accusation now waits.
When Torvald finally reads the letter, the marriage shatters in minutes. He does not thank Nora for the sacrifice that once saved him; he rages that she is a liar and a criminal who has ruined his future, declares she is unfit to raise their children, and resolves only to hush the matter up and keep her on for appearances. Then a second letter arrives in which Krogstad, softened by a reunion with Mrs Linde, returns the bond, and Torvald instantly forgives everything and calls Nora his frightened songbird again.
But the few minutes of his fury have shown Nora exactly what her marriage is. For the first time the two sit down to a serious conversation, and she tells him she has been his doll-wife as she was once her father's doll-child, never asked to think for herself. She no longer believes the duties of wife and mother outrank her duty to become a reasonable human being. Refusing his help and his name, she lays down her keys and leaves to find out who she is, and the play ends on the sound of the front door closing behind her.