The film’s climax centers around the resolution of the Vanger family mystery, involving the disappearance of Harriet Vanger, niece to wealthy industrialist Henrik Vanger (Christopher Plummer).
After months of investigation, Mikael and Lisbeth uncover a series of old photographs that lead them to the realization that Harriet is alive and hiding in Australia. They conclude that Harriet faked her own death to escape her abusive brother Martin (Stellan Skarsgård), who was responsible for the other Vanger family murders.
Meanwhile, Martin, who has been observing Mikael and Lisbeth’s investigation, becomes aware that they are closing in on the truth. In a tense confrontation, Lisbeth confronts Martin at his secluded home. Martin attempts to overpower her, but Lisbeth gains the upper hand, ultimately incapacitating him.
Mikael, with the help of a Vanger family reunion, exposes Martin as the murderer responsible for the gruesome crimes. Lisbeth records a confession from Martin, admitting to the murders and the horrific abuse he subjected her to when she was a child.
In the aftermath, Harriet returns to Sweden to reclaim her family’s company. Lisbeth decides to leave the country, taking the vast amount of money she acquired through hacking to start a new life. She leaves a parting gift for Mikael, who is now back at the investigative magazine Millennium, by solving the mystery of another case.
The film concludes with Mikael continuing his work as a journalist and receiving a message from Lisbeth, hinting at a future reunion. The ending leaves room for the continuation of Lisbeth and Mikael’s complex and compelling partnership.
The film is noted for its dark and intense themes, intricate plot, and Rooney Mara’s standout performance as Lisbeth Salander. The unresolved aspects at the end also set the stage for potential sequels based on Stieg Larsson’s “Millennium” book series.