CEO of the family business, disappeared and was presumably murdered by someone in the family. Vanger offers Blomkvist a significant fee and damning information about Wennerstrom if he will conduct an investigation into Harriet’s disappearance. Blomkvist accepts the offer and goes to live on the island after he serves his short prison term.

Because she was institutionalized for most of her teenage years, Salander is required by the court to have an appointed legal guardian who controls her finances and must approve any large expenses. Holger Palmgren is both her guardian and trusted friend; just as he is prepared to legally emancipate her from any kind of guardianship, he has a debilitating stroke and the change is not made. Nils Bjurman is appointed as her new guardian, but the first time she meets with him he takes sexual advantage of her, assuming she is weak and abusing his position of authority. He threatens her into silence with her own money.

When he violently rapes her the next time she has to see him, Salander is prepared. She records the episode and uses the tape to exact her revenge. It takes her some time to recover; however, once Bjurman is smug in his ability to control her, Salander visits his apartment when he is most vulnerable and demands he relinquish all control over her life. She abuses him in much the same way he abused her and then tattoos his chest, marking him as a rapist so he will not be able to hurt anyone else.

Blomkvist needs a research assistant, and he chooses Salander because she has managed to hack into his computer and has offered him anonymous clues to his investigation. They work well together, for Blomkvist allows Salander to be herself without placing any demands on her. They become lovers and soon discover much more than a potential murder by a family member motivated by money or jealousy. After examining folders, files, and photos, they both realize they are searching for a serial killer who has victimized women for more than forty years. One of the hallmarks of these murders is the use of scripture references from Leviticus.

Salander and Blomkvist are living in a cottage on the island, and soon they realize that someone has broken in and examined their research. Blomkvist visits several family members, all of whom had reason to want Harriet dead. In Vanger’s files, Blomkvist discovers a photo which might be a clue to what happened to Harriet. After Blomkvist is nearly killed by an unknown assailant, he becomes suspicious and goes to see Martin, Harriet’s brother and current CEO of Vanger Corporation. Martin has prepared for this visit, though, and he drugs Blomkvist before dragging him down to a secret room in his cellar. Blomkvist wakes up to find that Martin has tied him up in a place designed for torture; it is then that Martin explains how he came to be a serial stalker and murderer of women.

Martin’s father was a religious fanatic who, early on, molested Martin and then taught Martin how to rape and strangle women. Martin produces photos and brags to Blomkvist about all the women he has mutilated and strangled over the years, taking whatever he wanted as his father taught him. Martin places Blomkvist in a noose and prepares to hang him.

In the meantime, Salander is researching in the Vanger Corporation’s archives; she finds evidence leading her directly to Martin and rushes back to Hedeby to warn Blomkvist about Martin. When she arrives at the cottage, she discovers that Blomkvist is gone and checks the surveillance tape on the equipment she insisted they install. She rushes immediately to Martin’s house where she arrives just in time to free Blomkvist by beating Martin with a golf club. Blomkvist survives, but he was close to dying. The wounded and terrified Martin drives away and steers directly into an oncoming truck, committing suicide.

Blomkvist and Salander find Anita, Harriet’s look-alike cousin, living in London; they discover from her that Harriet is alive and living in Australia. Blomkvist goes to visit her and Harriet tells him what caused her to leave her home and family so many years ago. Her father and Henrik’s brother, Gottfried, used to rape her repeatedly and her brother Martin was forced to do the same until he grew to have a perverse satisfaction in humiliating his sister. Harriet finally seized the opportunity to drown her father in self-defense.

Everyone assumed the death was an accident, but Martin saw what she did and continued the sexual abuse until Harriet was sent away to boarding school. On the day she disappeared, Harriet had returned to the island and saw Martin again, she knew she had to leave before the abuse resumed. She confided in her cousin Anita and she was willing to help her out of the country. Harriet took advantage of an accident on the island and, in the confusion, escaped Sweden with Anita’s help. After spending a few years in a convent, Harriet has been living in Australia, widowed with children and running a large, successful international corporation.

Every year since she left, Harriet sent her beloved uncle a dried flower in a frame, hoping it was sending the subtle message to him that she was still alive. Blomkvist convinces her to come home to see Henrik after assuring her that Martin is dead. Harriet and her uncle Henrik are reunited and Henrik initiates plans to establish Harriet as the next CEO of the Vanger Corporation.

As promised, Henrik gives Blomkvist the information he has on Wennerstrom; unfortunately, the information is decades old and virtually unusable. Salander, an expert and ingenious computer hacker, downloaded the entire contents of Wennerstrom’s computer and now gives Blomkvist much more damning information on the corrupt businessman.  

Both Salander and Blomkvist benefit from this information. Salander learns that Wennerstrom has treated his young girlfriend poorly,  forcing her to get an abortion, and exacts revenge on the girl’s behalf by stealing billions of kroners from Wennerstrom’s accounts and depositing them in several false accounts she created. Salander determines to give some of that money to the victims of Martin’s heinous crimes. Blomkvist writes an expose for his magazine and a book which receives international attention, saving Millennium from financial ruin and eventually restoring his reputation as an incisive journalist.

Wennerstrom goes into hiding. Blomkvist sees a picture on television of the woman who so artfully stole all of Wennerstrom’s money; he recognizes Salander in disguise and is proud of her. Blomkvist becomes famous for exposing Wennerstrom and speaks out publically wherever he can, blasting financial reporters for allowing Wennerstrom to inflate his worth and become so powerful. Wennerstrom refuses to speak to the media except through his lawyer, and then he disappears.

No one ever asks Salander where Wennerstrom is, but she could have told them. For six months, Salander monitors Wennerstrom’s movements by watching his computer. She leaves a message regarding his whereabouts for one of the Columbians to whom Wennerstrom owed money—but which he was unable to pay because she took it all. Wennerstrom is found dead in Spain a few days later, with three bullet holes through his head, and Salander is not surprised.

Blomkvist has a cabin to which he generally retreats alone, but he and Salander spend Christmas there together. Salander comes to the realization that she is love with Blomkvist and this vulnerability terrifies her. Finally Salander realizes she is ready to allow Blomkvist into her extremely private world and decides to tell him how she feels. When she goes to see Blomkvist, she sees him walking with Erika Berger, his co-publisher. Berger and Blomkvist are also long-time friends and lovers, and when she sees them walking together into Blomkvist’s apartment, Salander is so upset that she wants to hit them. She walks back to her apartment alone in the snow.