The Girl with the Dragon Tattoo

Mikael Blomkvist and Lisbeth Salander eventually piece together that Harriet Vanger's brother Martin, now CEO of Vanger Enterprises, has spent years abusing and murdering women, a pattern of violence instilled in him by his late father Gottfried, who had sexually abused both Martin and Harriet as children. When Blomkvist confronts Martin, Martin overpowers him and drags him to a hidden torture chamber in his home, intending to kill him. Lisbeth arrives just in time, breaking in and freeing Blomkvist. Martin flees by car and dies when he crashes into a truck on the highway, an apparent suicide.

With Martin dead, Blomkvist and Lisbeth realize Harriet was never murdered at all: she ran away decades earlier to escape her sadistic brother. They track her down in Australia, where she has been quietly running a sheep farming business. When confronted, Harriet confirms their reconstruction of events and admits that she was responsible for the death of her father Gottfried, which had been treated as an accident. She agrees to return to Sweden, where she is warmly reunited with her elderly great-uncle Henrik Vanger and steps into a leading role in the family company, which lost its CEO with Martin's death.

The secondary plot involving financier Hans-Erik Wennerström, who had successfully sued Blomkvist for libel and gotten him sentenced to prison, resolves separately. Henrik Vanger's promised evidence against Wennerström proves thin, largely a device to lure Blomkvist into taking the Harriet assignment. However, Lisbeth independently hacks into Wennerström's computer and uncovers evidence of much larger financial crimes than Blomkvist had originally reported. Using this material, Blomkvist publishes a major exposé and a book that ruin Wennerström and vindicate Blomkvist, elevating both him and Millennium to national prominence.

The book closes with Blomkvist's professional reputation restored and his magazine thriving, while Lisbeth Salander, who has grown close to him during the investigation, is left in a more ambiguous personal position as the story ends.

Mikael Blomkvist is a Stockholm journalist and co-owner of the magazine Millennium. As the book opens, he has just lost a libel case against billionaire industrialist Hans-Erik Wennerström and is sentenced to three months in prison; he steps down from Millennium's board, over the objections of his close friend, sometime lover, and business partner Erika Berger.

While awaiting his sentence, Blomkvist is hired by elderly retired industrialist Henrik Vanger to write the history of the wealthy but dysfunctional Vanger family, ostensibly for a large fee and (crucially to Blomkvist) Vanger's promise of damaging evidence against Wennerström. The real assignment, kept secret, is to investigate the disappearance nearly 40 years earlier of Henrik's great-niece Harriet Vanger, whom Henrik believes was murdered by someone in his own extended family, since he has received an anonymous, taunting gift of pressed flowers every year on his birthday since her disappearance, mimicking a tradition Harriet had with him.

Lisbeth Salander is a young, brilliant, socially isolated computer hacker and professional investigator, first introduced when Vanger's firm hires her to background-check Blomkvist. She is later brought openly into the investigation to assist Blomkvist with research, and the two become both investigative partners and, for a time, lovers.

Together they uncover that Harriet's brother Martin Vanger, the current CEO of Vanger Enterprises, has for years been abusing and murdering women, having been indoctrinated into sadistic violence by their father Gottfried, who had also sexually abused both Martin and Harriet. Martin captures Blomkvist and is about to kill him when Lisbeth intervenes and saves him; Martin flees and dies in a car crash, apparently by suicide.

Blomkvist and Lisbeth then discover that Harriet was not murdered but fled the family decades ago to escape Martin's abuse, and has been living in Australia running a sheep farm. She admits she caused her father Gottfried's death, long assumed accidental. She returns to Sweden, reconciles warmly with Henrik, and takes on a leadership role in the now leaderless family company.

Separately, the promised evidence against Wennerström turns out to be weak and largely a lure to secure Blomkvist's cooperation, but Lisbeth independently hacks Wennerström's systems and finds proof of extensive financial crimes. Blomkvist uses this to publish an exposé and book that destroy Wennerström's reputation and restore Blomkvist's own standing, propelling Millennium to national prominence.

By the book's end, Blomkvist's career and Millennium's fortunes have been fully rehabilitated, the Vanger family mystery is resolved, and Martin and Gottfried's crimes have been exposed within the family circle (though not made public). Lisbeth Salander remains a singular, guarded figure whose personal life, past, and long-term relationship with Blomkvist are left open and unresolved as the story closes.