The English language title refers to the major plot of the story – Lisbeth Salander, with lots of help from her friends, takes on the hornet's nest of lies and deceit which has made her life miserable for years. The main hornets who live in the nest: Peter Teleborian, the psychiatrist who is obsessed with Salander; her father, Alexander Zalachenko, former Russian spy and head of an international sex/drug trafficking ring; the Section, a secret group inside the Swedish Security Police who will protect the secrets of Zalachenko by any means.
The original Swedish title is Luftslottet som sprängdes or The Air Castle That Was Blown Up. It doesn't focus on Salander like the English language title. Maybe this is because taking down the Section and Teleborian is a group effort. To blow up the air castle, to shatter the illusions that are allowing the victimization of Salander and hundreds, maybe thousands of children, lots of people need to be invested in bringing the truth to light.
We see cooperation between The Constitutional Protection Unit of the Security Police, Millennium magazine, Milton Security, members of the police force, and the Hacker Republic. Blomkvist acts as ace diplomat negotiating between and protecting the different parties. In spite of the seeming hopelessness of the problems presented in this trilogy, the final installment shows a deep faith in humanity, and in our ability to work together toward a common good.