US author Dan Brown announced on Facebook and Twitter Tuesday "Inferno," his fourth book in "The Da Vinci Code" series, is to be published in May. The mystery novels follow the adventures of Harvard University symbologist and crime-solver Robert Langdon. The BBC quoted Brown as saying "Inferno" is set in Italy and will see Langdon drawn into "a harrowing world centered on one of history's most enduring and mysterious literary masterpieces." "Although I studied [poet] Dante's 'Inferno' as a student, it wasn't until recently that I came to appreciate the enduring influence of Dante's work on the modern world," Brown said. "With this new novel, I am excited to take readers on a journey deep into this mysterious realm; a landscape of codes, symbols, and more than a few secret passageways." Brown's Langdon novels have sold millions of copies worldwide and two of them - "The Da Vinci Code" and "Angels and Demons" - have been adapted as blockbuster films starring Tom Hanks as Langdon. A movie version of "The Lost Symbol," the third book in the series, is in development.