The Girl With the Dragon Tattoo's Prologue features an unnamed man (who we soon learn is Henrik Vanger) getting a framed, pressed Australian flower in the mail on his birthday, November 1st. He calls Detective Superintendant Morrell and tells him about the flower. Henrik gets one of these flowers every year on his birthday. He has a total of 44 now. But he and the detective can't solve the mystery of who exactly keeps sending them. This thought makes Henrik cry.
After the Prologue, a copy of the Vanger family tree is provided for the readers. The rest of the novel is divided into four parts plus an Epilogue. It moves from December 20, 2002 to December 30, 2003.
Welcome to Stockholm, Sweden. It's a Friday in late December 2002. And it's cold.
Meet 42-year-old Mikael Blomkvist, a financial journalist, and managing editor of Millennium magazine, devoted to exposing financial corruption. Blomkvist has just been convicted of publishing libelous material about financier Hans-Erik Wennerström and has been sentenced to a hefty fine and three months in prison, which he'll serve some time in 2003.
Next we meet 24-year-old Lisbeth Salander, private investigator extraordinaire, and her boss at Milton Security, Dragan Armansky. Armansky and Salander are meeting with Dirch Frode, who hired Milton to investigate Mikael Blomkvist. Salander tells Frode that Blomkvist doesn't seem to be corrupt. He's a good journalist. But she still thinks Wennerström is crooked and that Blomkvist was set up. She agrees to investigate Wennerström for Frode. She tells Frode that Blomkvist is divorced with a teen daughter, and that he has a longtime sexual relationship with Erika Berger, editor-in-chief of Millennium. Erika is married but her husband, artist Greger Beckman, doesn't mind her relationship with Blomkvist. In all, Salander paints Blomkvist in a positive light.
Blomkvist and Berger meet at the Millennium offices, and Blomkvist convinces Berger to temporarily fire him, so his conviction will have less of a chance of hurting the magazine. Berger reluctantly agrees. Now that that decision's out of the way, Berger and Blomkvist spend the weekend together making love.
On Monday, Blomkvist goes over to Millennium, which is closed for the holidays. While he's there, he gets a call from Dirch Frode who says he represents Henrik Vanger, patriarch of the Vangers, a wealthy industrial family that owns the Vanger Corporation. The current CEO of the Vanger Corporation is Martin Vanger. Frode says Henrik wants to hire Blomkvist for something, but he can't say what. Henrik wants Blomkvist to come meet up on remote Hedeby Island because he's too old to travel.
On Christmas Eve, Salander takes presents to her 46-year-old mother in a nursing home. Salander and her mother briefly discuss the fact that neither of them have seen Salander's sister, Camilla, in a long time. Before Salander leaves, her mother mistakes Salander for her sister Camilla.
Blomkvist visits his ex-wife and his daughter, Pernilla, on Christmas Eve and then goes to his sister's place. At his sister's, he decides to accept Frode's offer and agrees to go to Hedeby Island. The day after Christmas he goes to Hedeby and meets Henrik Vanger.
Meanwhile, Salander goes to Hans-Erik Wennerström's apartment building. She checks out the electrical room and finds the wiring to Wennerström's apartment. Next, she visits her hacker friend Plague and buys an electronic cuff from him. (The cuff is a hacking device; Salander explains how she uses it in Chapter 28. It's implied, at this point, that Salander uses the cuff to do something to the wiring in Hans-Erik Wennerström's apartment.)
Back to Hedeby Island, Blomkvist learns that Henrik's great-niece, Harriet Vanger, disappeared 36 years ago. She started giving him pressed flowers when she was eight. After her disappearance, Henrik continued getting flowers in the mail. He's convinced Harriet was murdered by a family member, here on the island, and that her killer sends the flowers to torment him.
To persuade Blomkvist to investigate Harriet's disappearance, Henrik offers Blomkvist a big chunk of cash, and the promise of information that will allow Blomkvist to expose Hans-Erik Wennerström as a corrupt financier. Although he thinks it's a mistake, Blomkvist agrees to spend a year on Hedeby Island, helping Henrik write his autobiography and trying to find out what happened to Harriet. Erika Berger is extremely upset. She feels like Blomkvist is abandoning her.
On January 3rd, Salander gets a call from Dirch Frode telling her to stop her investigation of Wennerström. But, little does he know, Salander doesn't like stopping investigations once she starts them.
Blomkvist arrives at Hedeby Island on January 3rd. Henrik gives him a tour and points out some of the major suspects in the disappearance of Harriet Vanger all those years ago. Harald Vanger is Henrik's 92-year-old brother, a hermit and lifelong member of the Nazi party. Henrik doesn't speak to him. Isabella Vanger is 75 years old, and the mother of Harriet. She was a hands-off mother with few parenting skills. Cecilia Vanger is 56, which means she was 20 when Harriet disappeared. She's Harald's daughter but has nothing to do with the guy. Henrik likes her. Her sister, Anita, lives in London.
Martin Vanger is 54, is Harriet's brother, and Vanger Corporation CEO. Martin built his current home in 1978 when he replaced Henrik as CEO. He's not married. Martin was stuck on the other side of the island (due to an accident on the bridge) when Harriet disappeared on September 24, 1966, so he was off the hook. Martin and Harriet's father, Gottfried, drowned in the lake near his remote cabin on Hedeby Island the year before Harriet disappeared.
During the rest of January, Blomkvist gets friendly with Martin Vanger and even has dinner at his house with Erika Berger and Martin's girlfriend Eva.
Meanwhile, Salander, who was in a psychiatric institution for several years as a teen, is getting to know her new guardian, Nils Bjurman. (Salander is one of a minority of adults in Sweden under guardianship. She was deemed incapable of handling her own affairs and thus assigned a guardian who is legally permitted to make decisions on her behalf, and who has all the legal powers she would normally have herself. How Salander got into such a mess is revealed in The Girl Who Played With Fire.)
Salander's old guardian was Holger Palmgren, and Palmgren helped Salander have a stable life by getting her a job at Milton Security. But Palmgren had a stroke in December and Salander believes he never recovered from it. Her new guardian, Nils Bjurman, has taken away Salander's access to her bank accounts. He has also asked her inappropriate questions about her sex life. Hm.
In February, Berger and Henrik make a deal and Vanger Corporation becomes a partner with the financially-hurting Millennium. Blomkvist is mad because Henrik and Erika have been plotting the deal for weeks behind his back. Making the deal without him is Erika's revenge on Blomkvist for leaving her alone in Stockholm to deal with Millennium. But Blomkvist soon gets over his anger and instead gets deeper into the mystery of Harriet. He's also seduced by Cecilia Vanger, and they become lovers. To Cecilia's dismay, he prepares to begin his prison term and work on Harriet's case while he's in the clink.
Meanwhile, Salander's computer gets run over, so she has to ask Bjurman to release some of her funds so she can buy a new one. He forces her to perform oral sex, and then gives her the money. She plans to kill him, but then decides to get revenge and control instead.
In early March, Salander meets Bjurman at his house, using herself as bait so she can film Bjurman raping her and then blackmail him. But Bjurman takes it much further than she thought he would. He handcuffs her to the bed, rapes her brutally, and holds her captive for about eight hours.
Still, she returns to Bjurman's house a week later. She tasers him, ties him to the bed, tortures him, and shows him the film of him raping her (her rucksack has a camera on the buckle). She tells him how it's going to be now, and tattoos the words, "I AM A SADISTIC PIG, A PERVERT, AND A RAPIST" (14.93) all over his front side.
Blomkvist gets out of prison in May and restarts his affair with Cecilia Vanger. But, after Erika Berger surprises Blomkvist in bed with Cecilia, Cecilia decides to break things off. In June, Blomkvist starts to make progress on Harriet's case, and he decides he needs help in his investigation. Dirch Frode recommends Salander, and lets it slip that she investigated Blomkvist. Blomkvist demands the report and then sets off to meet Salander. He surprises her, but she accepts the job as his research assistant.
In July, Salander identifies a series of women who were murdered and raped between 1949 and 1966, and who are referenced in Harriet's date book, which she left behind. Blomkvist and Salander decide there must be a connection between the Vanger family and these bizarre murders, which often involved animal sacrifice.
Also in July, Salander seduces Blomkvist and they begin sleeping together. One morning they find the mutilated, charred corpse of Tjorven, the Hedeby Island cat that befriended Blomkvist. Shortly thereafter, someone tries to shoot Blomkvist while he's jogging, resulting in a head injury from concrete shrapnel, but amazingly no loss of life or limb.
Finally, Blomkvist realizes, courtesy of some photographs, that Harriet was frightened of her brother Martin the day she disappeared. He goes over to Martin's to confront the guy, and Martin chains him up in his basement. While held captive, Blomkvist learns that Martin's father Gottfried killed the women referenced in Harriet's date book, raped Martin, and taught Martin to rape and kill women too. After Gottfried's death, Martin became a serial killer himself, and uses his basement on Hedeby to torture and kill the women. Surprisingly, Martin doesn't know what happened to Harriet.
Martin is about to rape Blomkvist, and will surely kill him after, when Salander bursts in and saves him. Then she hops on her motorcycle to pursue Martin, who's getting away in his car. Martin drives his car into an oncoming truck and dies.
While Blomkvist gets some rest, Salander goes back to Martin's place and photographs the scene. Then she destroys some of the evidence of his crimes. She informs Dirch Frode of what has transpired, but says that neither her name nor Blomkvist's are to be given to the police if Frode chooses to report Martin's crimes.
Salander and Blomkvist realize that Cecilia's sister, Anita, is connected to Harriet's disappearance and they fly to London to talk to her. Through her they track Harriet Vanger to Australia, where she's living as Anita Cochran. But then Salander's mother dies, and Salander flies back to Stockholm. Blomkvist, however, sets out for Australia. He meets Harriet and learns the truth.
Her father Gottfried and brother Martin began raping Harriet when she was fourteen. When she was fifteen, she killed her father. Martin caught her and used the information to make her his sex slave. Martin went away to school. When he returned on September 24, 1966, Harriet was terrified. So she ran away with the help of her cousin Anita. In Italy, Harriet met Australian Spencer Cochran. They got married and have three kids and a happy life on Spencer's prosperous sheep farm. Harriet sends a framed, pressed flower to Henrik every year on his birthday, hoping to send him the message that she's alive and well.
After Harriet returns to Hedeby, Blomkvist agrees (against his will) to cover up Martin's crimes to spare Harriet and the Vanger Corporation public disgrace. Salander and Blomkvist turn their attentions to the Wennerström affair. Salander reveals that by using the electronic cuff she bought from Plague, she has successfully hacked Wennerström's computer. She has control over it and access to all of its contents. All of his financial records are in his computer and she can see all his banking information. Using the information in Wennerström's computer, Blomkvist spends months writing a book and lengthy article about Wennerström. Salander studies Wennerström's finances carefully, and then flies to Zurich and manages to steal millions of dollars from him.
Blomkvist's book on Wennerström, called The Mafia Banker, and Millennium's exposé clear Blomkvist's name and expose one of the biggest financial frauds in Swedish history. Wennerström disappears and evades authorities. But he doesn't evade Salander. Wennerström is still using the same computer she hacked. When the authorities give up the chase, she makes a quick phone call and the next thing you know, Wennerström is dead.
Salander and Blomkvist spend much of the Christmas holiday together. She realizes she's in love with him. After Christmas, she decides to go to his place without calling. She buys him a late Christmas present, a metal Elvis sign with the words "Heartbreak Hotel" (Epilogue.128).
On her way to his apartment, though, she sees him with Erika Berger and has a jealous rage. She walks away, tossing Blomkvist's present in the trash. And that's the end.