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 translators and editors have read the whole 500-page novel 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.”
Devoted readers are keenly awaiting the thriller. The first three Millennium books, published in 2005-2007, have sold 80 million copies worldwide and have been made into Swedish and Hollywood movies.
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 two 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 news agency AFP in February, saying he 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 that 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 27th.
But some accuse Norstedts, Stieg Larsson's heirs and David Lagercrantz of milking a cash cow.
In Swedish newspaper 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.
“Every publishing house in the world publishes books to make money. They're not charities,” countered Altrov Berg.
Norstedts will not utter a word on the book's expected sales.
Larsson's heirs have however said they plan to donate the royalties to the anti-racist magazine Expo, co-founded by Stieg Larsson.
For literary critic Mats Svensson, the money issue is typical of Swedish publishers' increasingly aggressive business strategies.
“The big Swedish publishing houses, just like the Anglo-Saxon ones, are increasingly being run like regular businesses, expected to produce high returns and rising sales… Norstedts … has gone from churning out books to churning out profits,” Svensson lamented.
“This is a book commissioned by the survivors and the publisher. They want to continue to make money off the franchise that's been built up around the Millennium trilogy,” agreed Sara Karrholm, a literature professor at Lund University.
The novel should have no trouble finding an audience, she said.
“There are so many people who liked the characters … and want to know what becomes of them.”
“You can sort of compare the Millennium sequel to a new season of a TV series: you want to follow it because you want to continue your acquaintance with the characters,” Karrholm said.
Norstedts insists it has no plans for a fifth installment, and tried to tone down the hype a few days before the release date.
“It's just a book. The readers will decide,” Altrov Berg said.
Around 2.7 million copies go on sale in 25 countries on Thursday, and in the US on September 1st.