STOCKHOLM: With secret codes and locked-down communication, Swedish publisher Norstedts has kept the plot of the sequel to the best-selling Millennium crime trilogy, due out on Thursday, shrouded in secrecy.

The mystery is fitting for the sci-fi spy intrigue entitled “The Girl in the Spider’s Web,” the highly-anticipated dark thriller penned 11 years after the death of the series’ creator Stieg Larsson.

Only a few people have read the 500-page tome — just translators and editors — that takes up the story of tattooed computer hacker Lisbeth Salander and journalist Mikael Blomkvist.

And Norstedts has given fans only a small sneak preview.

“One night professor Frans Balder, a leading authority within AI (artificial intelligence) research, calls up Blomkvist,” it wrote on its website.

“Balder says he has world shattering information on US intelligence services. He has also had contact with a female super hacker, who bears a certain resemblance to a person Blomkvist knows well.”

The thriller is keenly awaited by devoted readers. The first three Millennium books, published in 2005-2007, have sold 80 million copies worldwide and have been made into Swedish and Hollywood movie adaptations.

But before the fourth installment even went to press it was already enveloped in scandal.

Among the book’s detractors is Eva Gabrielsson, who was Stieg Larsson’s partner of 32 years until he died suddenly of a heart attack in 2004 at age 50.

The couple were not married and Larsson left no will, so his estate went to his brother and father. Gabrielsson, 61, lost a bitter battle with them to manage his work.

To write the trilogy’s sequel, Larsson’s brother and father chose David Lagercrantz — a Swedish journalist known for writing football star Zlatan Ibrahimovic’s official biography — a “totally idiotic choice,” Gabrielsson told AFP in February, saying she knew nothing of the milieu Stieg Larsson described in the books.

The writing of the novel was shrouded in secrecy, with the author, editors and translators working on computers disconnected from the Internet to avoid leaks.

“We saw how Sony Pictures got hacked in 2013 and we didn’t want to get hacked,” Norstedts spokeswoman Linda Altrov Berg told AFP.

“We have made things more expensive for ourselves,” she said in her office near Stockholm’s Old Town.

For the translations, the novel was delivered by courier to the publishing houses who owned the rights to the first three volumes.

A slew of confidentiality agreements were signed, and no interview with the author can be printed before the book is released on August 27.

But some accuse Norstedts, Stieg Larsson’s heirs and David Lagercrantz of milking a cash cow.

In Sweden’s paper of reference Dagens Nyheter, Stieg Larsson’s childhood friends recently compared the publication of the fourth tome to “grave robbing.”

Norstedts has rejected the criticism, saying the novel doesn’t tarnish Stieg Larsson’s memory.

Altrov Berg insisted Lagercrantz was not like a “ghostwriter who imitated Stieg’s voice. It’s his own book.”

In Eva Gabrielsson’s eyes, the book is only seeing the light of day because of greed.