It is based on Dante's Inferno, and the linguists who translated Dan Brown's new blockbuster novel from English into other languages lived in distinctly underworld conditions, it has emerged.
For two months, 11 translators of different nationalities were tucked away in an underground bunker near Milan where they worked under the strictest security to translate Brown's new book into French, German, Italian and other languages for its simultaneous release on May 14.
When they arrived in February last year, they were put into "lockdown", as one official put it. Their mobile phones were confiscated and they were placed under strict instructions to reveal nothing of the plot.
The translators had limited access to computers, were banned from taking any notebooks or papers out of the bunker and had to hand in the manuscripts they were working on each evening.
Minibuses transported them to and from the hotels they were staying in. They were accompanied by security guards and ate in a staff canteen in the headquarters of Mondadori, the Italian publishing giant that is owned by Silvio Berlusconi.
Each was given an alibi and cover story to offer to anyone who showed too much curiosity about what they were doing all day down in the bunker.
The extraordinary security measures and the translators' strange experience were revealed in an Italian magazine, TV Sorrisi e Canzoni, which is owned by Mondadori.
Carole Del Port, a French translator, said: "The time outside the bunker was essentially reduced to nothing - lunch, dinner at a very late hour and sleep.
"But it was a unique, fantastic experience - a rare opportunity to work in a group for weeks and to experience total immersion in the world of Dan Brown."
One translator joked: "I'm not allowed to tell you anything about it. If I did I'd have to shoot you."
Inferno is the latest book by Dan Brown to feature his hero, Harvard "symbology" expert Robert Langdon, who was played by Tom Hanks in the film versions of The Da Vinci Code and Angels and Demons.
In an Amazon entry the plot is summarised: "Robert Langdon, is drawn into a harrowing world centred on one of history's most enduring and mysterious literary masterpieces.
Drawing from Dante's poem, Langdon races to find answers and decide whom to trust ... before the world is irrevocably altered."