The film commences in Sweden, showcasing a young Lisbeth Salander (Beau Gadsdon) engaged in a game of chess with her sister Camilla (Carlotta von Falkenhayn). In a tense moment, one of Camilla's pieces topples, revealing a spider that crawls out. Shortly thereafter, their father Alexander Zalachenko (Mikael Persbrandt) enters and demands the girls come to his room. He comments on Camilla's growth, pulling her beside him, which raises Lisbeth's alarm about his inappropriate intentions. In a panic, Lisbeth seizes Camilla’s hand and retreats to their room. Eventually, she climbs out onto the balcony, preparing to leap into the unknown. Camilla, compelled by their father's orders, stays behind, leaving Lisbeth no choice but to jump, sliding down the hill and escaping her oppressive home life forever.
Two decades later, the narrative shifts to a despicable CEO in Sweden who has physically assaulted his wife. As the lights in his home go out, he is shocked to find Lisbeth—now portrayed by Claire Foy (claire-foy)—standing before him cloaked in a dark hood and unsettling makeup. In a spectacular display of retribution, she tips over a statue that ensnares his legs, hanging him upside down. With precise knowledge of his immoral acts—including abusing two prostitutes and an affair with a married woman—Lisbeth reveals that she has siphoned his funds into their accounts, provided they grant her the necessary codes. The wife reluctantly complies, driven by fear, as Lisbeth threatens to expose a compromising video if he dares contact them again. With chilling calmness, she departs, leaving the man in a pitiful state of panic.
Meanwhile, Mikael Blomkvist (Sverrir Gudnason) arrives at Millennium Magazine, expressing discontent with its new ownership. A discussion with publisher Erika Berger (Vicky Krieps) ensues, as he invites her to meet later, but she declines due to commitments with her husband.
Lisbeth's life takes a turn when she shares an intimate encounter with Sofia (Andreja Pejic). Browsing through Lisbeth's photos, Sofia stumbles upon one of the sisters as children, leading Lisbeth to revealingly express her relief over Camilla and their father's deaths. Yet, she swiftly dismisses Sofia to attend to urgent matters.
Lisbeth soon connects with Frans Balder (Stephen Merchant), a contractor who previously worked with the NSA. He divulges the existence of a perilous program he created called Firefall, capable of accessing nuclear launch codes. Realizing the catastrophic potential in the wrong hands, Balder enlists Lisbeth's help to reclaim it from the NSA.
At NSA headquarters, security expert Edwin Needham (Lakeith Stanfield) detects an unauthorized breach. Despite his attempts to shut down the system, Lisbeth eludes capture and absconds with Firefall, leaving behind a mocking image.
However, the peril escalates when masked assailants attack her apartment, shooting her and nearly causing her demise in an explosion. The police arrive as Lisbeth manages a daring escape on her motorcycle, driving off into the frozen landscape.
The narrative thickens as Balder, witnessing the explosion, mistakenly believes Lisbeth betrayed him. In response, he reaches out to Gabriella Grane (Synnøve Macody Lund), who operates within the Swedish Secret Service. Meanwhile, Needham’s motivations are scrutinized as he arrives in Sweden, claimed to be on vacation, but Grane remains suspicious.
Lisbeth seeks refuge with Plague (Cameron Britton), an ally, as she escalates her investigation alongside Mikael. They uncover a connection to a violent group known as the Spiders, tied to the past horrors inflicted by their father.
The stakes rise when Needham finds a clue linking Sofia to Lisbeth, leading him to approach her with the intent of using her to locate Lisbeth. Meanwhile, as Lisbeth navigates the treacherous dynamics of the Spiders, she discovers that Camilla (Sylvia Hoeks), her sister, stands as the true puppet master behind the sinister plot to control Firefall.
In a climactic sequence, Lisbeth confronts her dark past as familial ties entwine with betrayal. The film reaches its tense conclusion as Camilla, consumed by her trauma, meets a tragic end, echoing Lisbeth's own desperate escape from their father's grasp.
As the story unwinds, Lisbeth finds a semblance of closure, ultimately returning to her home to orchestrate its destruction, watching the flames consume her past while riding away into the serene night, indicating her transformation and the unresolved complexities of her relationships.
