Act I opens in the Helmer’s tastefully furnished living‑room on a winter evening. Nora enters with parcels, a Christmas tree and a basket, pays the porter sixpence and hides the tree so the children won’t see it. She flirts with her husband Torvald, bragging about the money she has spent on gifts and revealing a new “little more reckless” attitude toward spending. Torvald, protective and patronising, chastises her spending and repeatedly calls her “little skylark” and “little squirrel”. He gives her ten shillings to the pound for household needs and asks what she herself wants; Nora pretends she wants nothing but eventually asks for more money to spend.

The children arrive with the nurse, and the household buzzes with Christmas preparations. Nora’s old school‑friend Kristine Linde (Mrs Linde) appears, having traveled from the countryside. The two women catch up; Kristine explains she is a widowed mother of two, tired of endless work, and now seeks employment. Nora, delighted, promises to find her a position with Torvald now that he will become bank manager. They discuss Nora’s secret: she confesses that she financed Torvald’s life‑saving trip to Italy by borrowing 250 pounds from Krogstad, forging her father’s signature on a bond, and repaying the loan in small installments. Nora claims the loan saved Torvald’s life but insists Torvald must never learn of it.

Krogstad, a former employee of the bank now in a precarious position, enters the room after the children have been sent away. He confronts Nora, reminding her of the forged bond and demanding that she use her influence over Torvald to keep his bank post. He threatens to reveal the forgery to the authorities, which would ruin Nora’s marriage and her reputation. Nora initially denies having any influence, then, in a sudden outburst, declares that she forged her father’s signature herself. Krogstad warns that the law will judge her regardless of motive. He threatens to expose her unless she secures his job.

Torvald returns, noticing Krogstad’s brief visit. He chastises Nora for lying about the visitor and warns her that a “songbird” must not sing false notes. He discusses his upcoming duties as the new bank manager, the need to reorganise staff during the Christmas week, and his plan to attend a fancy‑dress ball. He also expresses contempt for Krogstad, calling him a criminal who corrupts his children with lies. He extracts Nora’s promise not to intervene on Krogstad’s behalf, sealing his hand over hers. Nora, now terrified, clings to the Christmas tree, trying to maintain the festive façade while fearing the collapse of her secret.

The act ends with Nora’s frantic attempts to hide the tree, her pleading with the maid for help, and her desperate denial that the “horrible man” could ruin her family, as Torvald leaves to attend to paperwork and the children continue to beg to see their mother.