Lisbeth Salander, a brilliant hacker residing in Stockholm, is contacted by Frans Balder, a former NSA employee, to retrieve and destroy a dangerous program named FireFall that he developed. FireFall can access nuclear codes worldwide, and Balder fears it may fall into the wrong hands. With assistance from her long-time ally, journalist Mikael Blomkvist, Lisbeth successfully steals the program from the NSA but soon finds herself the target of a conspiracy involving the Swedish secret service, Russian cybercriminals, and a mysterious figure from her past.

As Lisbeth delves deeper into the web of intrigue surrounding FireFall, she discovers familial connections that complicate her mission. In the race against time, Lisbeth confronts numerous adversaries and leverages her hacking skills and resourcefulness to thwart those who seek to exploit the technology. Their journey reveals buried secrets and sparks a cat-and-mouse game through Stockholm's underworld. The stakes escalate as Lisbeth works relentlessly to protect those she cares about and dismantle the sinister plot threatening global security.