The Girl in the Spider's Web: Book 4

Lisbeth Salander and Mikael Blomkvist have not been in touch for some time. 

Then Blomkvist is contacted by renowned Swedish scientist Professor Balder. Warned that his life is in danger, but more concerned for his son's well-being, Balder wants Millennium to publish his story - and it is a terrifying one. 

More interesting to Blomkvist than Balder's world-leading advances in Artificial Intelligence, is his connection with a certain female superhacker. 

It seems that Salander, like Balder, is a target of ruthless cyber gangsters - and a violent criminal conspiracy that will very soon bring terror to the snowbound streets of Stockholm, to the Millennium team, and to Blomkvist and Salander themselves.