In Stockholm, Sweden, journalist Mikael Blomkvist, one of the co-owners of Millennium magazine, faces the repercussions of losing a libel case against the unscrupulous businessman Hans-Erik Wennerström. Simultaneously, the enigmatic Lisbeth Salander (/actor/noomi-rapace), a brilliant yet troubled hacker and researcher, undertakes an extensive background check on Blomkvist for the wealthy magnate Henrik Vanger, who has a critical task in mind for him. In return for valuable information about Wennerström, Blomkvist agrees to delve into the mystery surrounding the disappearance and presumed murder of Henrik's niece, Harriet, which occurred four decades prior.
After moving to the Vanger family's estate, Blomkvist stumbles upon a mysterious notebook filled with names and numbers that have long puzzled everyone. Harriet vanished in 1966, during a family gathering on a secluded island, where an accident blocked the sole bridge to the mainland for 24 hours. This tragic timing allowed one of the family members to carry out the horrific act.
Meanwhile, Salander, who is under legal guardianship due to diagnosed mental incompetency, confronts her abusive new guardian, lawyer Nils Bjurman, taking matters into her own hands in an unexpected and assertive manner. She cleverly manipulates Bjurman into giving her control over her finances after he misuses his power to exploit her.
As the investigation progresses, Blomkvist learns dark family secrets from Henrik about his brothers' connections to the Swedish Nazi Party and discovers that Harriet was the daughter of one of these notorious members. Blomkvist further analyzes clues hidden in Harriet's Bible, connecting the seemingly innocuous numbers to a series of murders of young women with Biblical names, all of whom are victims of the family’s malevolent legacy.
As Blomkvist and Salander collaborate on this dark mystery, their professional relationship intensifies into a romantic one, complicating the already intricate case. They discover that the last missing name on their list was a former secretary of Gottfried, Harriet's father, who was also found dead in suspicious circumstances.
In a thrilling confrontation, Blomkvist faces Martin Vanger, Harriet's brother and head of the Vanger group, who reveals his chilling history of violence against women. Just as the situation reaches a deadly climax, Salander intervenes, showcasing her resourcefulness and determination to protect Blomkvist.
As they delve deeper, Blomkvist begins to suspect that Harriet might still be alive, living under an assumed identity, hidden from her abusive family. The investigation reveals that she had been smuggled away by her cousin Anita, following a traumatic act of self-defense against her brother. Upon her return, Harriet finally reunites with Henrik, finding solace and safety at last.
In an unexpected turn of events, Blomkvist uncovers critical information about Wennerström, only to find that it leads to no genuine outcome. Salander, leveraging her hacking prowess, exposes Wennerström's crimes, ultimately aiding Blomkvist in publishing a damning article that ruins Wennerström’s reputation. However, as Blomkvist’s personal life unfolds, Salander feels a pang of heartbreak witnessing him with another woman, leading her to abandon her plans to celebrate Christmas with him.
