In Stockholm, Sweden, justice hacker Lisbeth Salander is employed by programmer Frans Balder to recover a program capable of accessing nuclear warhead codes in the world. The program is called Firefall, and he has developed it for the NSA, but Balder believes the code is simply too dangerous for it to exist. Lisbeth successfully recovers Firefall from the NSA servers, but draws the attention of an agent named Edwin Needham and fails to unblock him.
Later, the program is stolen by mercenaries led by Jan Holtser who are trying and killing Lisbeth. When she does not appear at the meeting she had planned in advance, Balder mistakenly believes that Lisbeth decided to keep Firefall for her and then contact Gabrielle Grane, Deputy Director of Swedish Secret Service. This moves Balder and his son, August, into a conspiratorial home to be safe.
Meanwhile, Needham detects unauthorized logging in Stockholm and arrives in hopes of finding Lisbeth and Firefall. Lisbeth asks her hacker friend, Plague, to help her and the two of them contact her ex-boyfriend, investigative journalist Mikael Blomkvist, to help them identify the attackers. Blomkvist finds out that Holtser has worked in the past for her late father, mafia Alexander Zalachenko, and is now in a hurry with an international criminal group known as “Spiders.”