"Robert Langdon's harrowing quest through Dante's underworld promises to be an exciting adventure of discovery. Florence makes a terrific setting. This is the place and Dante is the moment when the Renaissance begins," said Haag in a statement prepared by publisher Profile Books.

"I am excited to be close on the heels of Robert Langdon again and working with Profile Books on decoding the associations, the historical characters and the symbols in Dan Brown's new thriller."

There have been stirrings, too, from other Dan Brown guide authors: Simon Cox, author of "Cracking the Da Vinci Code" and "Hunting the Lost Symbol," promised his Twitter followers that details of his own guidebook would follow "very soon," while the Catholic World Report website teased its editor, Carl Olson, who was co-author of "The Da Vinci Hoax."