For a three-act plot analysis, put on your screenwriter’s hat. Moviemakers know the formula well: at the end of Act One, the main character is drawn in completely to a conflict. During Act Two, she is farthest away from her goals. At the end of Act Three, the story is resolved.
Act I
At first, Nora and Torvald Helmer seem... happyish. Torvald is overbearing, but Nora doesn't seem to mind. Torvald will soon start a new job as bank manager, which means more cash to play with.
The only grey cloud in the sky seems to be their friend Dr. Rank, who is slowly dying of tuberculosis of the spine. Nora's old friend, Mrs. Christine Linde, turns up. She's fallen on hard times. No worries, though, because Helmer gives her a job at the bank.
The troubles arise, though, when Krogstad arrives. Nora secretly borrowed money from him in the past to fund a trip that saved Torvald's life. In order to do so, she had to forge her father's signature. Krogstad is mad because Torvald wants to fire him from his job at the bank. He threatens to expose Nora if she doesn't convince Torvald to not fire him.
As the act draws to a close, Nora asks her husband to spare Krogstad's job. Torvald says he gets sick when he's around corrupt lawbreakers like Krogstad.
Act II
Act Two begins with Nora talking to her old wet-nurse, Anne. She asks Anne to look after her children if she's ever not around anymore. Ooh, that sounds ominous.
Nora makes a second attempt at begging Torvald for Krogstad's job. This attempt backfires. Torvald gets angry and sends Krogstad his notice. Nora is getting desperate. She begins to ask Rank for the money to pay off the loan, but feels guilty when he tells her that he will soon die and that he's in love with her. Krogstad returns, steaming mad about getting fired.
He tells Nora that he's going to blackmail both of them now. Krogstad plans to force Torvald into giving him an even better job than before. He drops a letter in the mailbox, detailing his demands to Mr. Helmer. Nora confesses everything to Christine, who runs off to try to appeal to Krogstad. At the end of the act, Nora dances a wild tarantella to distract Torvald from opening the mail. She convinces him that he must spend every waking second helping her practice her dance for the party the next night. Torvald agrees to not open the mail until after the party.
Act III
At the top of Act Three Christine is hanging out in the Helmers' living room by herself. Krogstad comes by. Christine tells him that she wants to be with him. He is super-happy and decides not to blackmail the Helmers anymore... but Christine tells him to let Torvald still receive the letter. She thinks there are too many lies between Nora and Torvald.
The Helmers return from the party, and Christine tells Nora that she needs to fess up. Dr. Rank stops by and intimates that he's dying. (What a fun evening.)
Nora eventually lets Torvald open his mail. When he reads Krogstad's blackmail letter, he goes nuts and calls her all kinds of awful things. A new letter from Krogstad arrives, saying that he's no longer blackmailing them. Torvald tells Nora he forgives her. Nora, however, doesn't forgive him. She tells him that she's leaving him because the "wonderful thing" didn't happen: he didn't try to sacrifice himself for her. She tells him that they've never had a real marriage. She's just been his doll-wife. At the end, Nora leaves, slamming the door behind her.