Da Vinci follow-up 'The Last Symbol' will be promoted with a series of puzzles

London, July 9 (ANI): Publishers of Dan Brown's new novel 'The Last Symbol' will be launching a series of puzzles, codes, and teasers on social networking sites like Facebook, as a part of their promotional campaign.

The book, which features Harvard Professor Robert Langdon for a third time, is due for release in September.

The storyline has still been kept under wraps, but it is believed to focus on freemasonry, with the lost symbol of the title a reference to a ciphered pictogram in an ancient book called The Key of Solomon.

The publishers have also revealed six million copies of the book will be printed on its first run, reports the BBC.

Brown had said that writing the new novel was "a strange and wonderful journey". (ANI)