By Tamsin Smith
BBC News, Rome
The faithful are flocking to Rome for Easter week, but the Vatican is also attracting pilgrims clutching blockbusters rather than bibles.
The book tourists have questions about the workings of the Church
Small clusters of Dan Brown fans carrying copies of his book Angels and Demons can be seen wandering around St Peter's Square.
They retrace the steps of a fictional hero in a murder mystery similar to the Da Vinci code.
"We are seeing increasing numbers of people coming to Rome from the UK and America just to do the tour and see the sites in the book," explains Simone Gozzi, head of Association Dark Rome that runs the Angels and Demons tour.
"We are even taking tour bookings from Italian school groups, which certainly surprised us."
Standing on the doorstep of the Vatican, one tour group hunts for signs and symbols hidden in the work of 17th-Century sculptor Gian Lorenzo Bernini.
The book uses his sculpture as clues pointing to a dastardly plot led by a secret society against the Roman Catholic Church - a threat to blow up the Vatican as the church elects a new pope.
Dan Brown's implication that Bernini was part of an anti-religious conspiracy has left some art historians fuming. Others though are more pragmatic.
"Its a nice idea for people to approach Rome and get to know Bernini, whose work is incredibly difficult to understand," says Professor Elizabeth Lev from Rome's John Cabot University.
"I think it would take a pretty dense tourist not to realise that there is something much grander going on in Bernini's work than a silly conspiracy theory described in a paperback thriller."
It is not just art Dan Brown fans are interested in. They listen avidly as their guide points to the Sistine Chapel, describing how cardinals elect a pope in a conclave
"The first time people arrive, they are full of questions for us about how the Vatican ticks," says Simone Gozzi. "Most people have never heard of a conclave before reading the book so are fascinated with how it works and they all want to know more."
American tourist Roy Diner is enthralled.
"It makes the myth even bigger by talking about the church and its politics because it reminds you how secretive it is," he says. "There are more questions than answers now for me."
"I came on this tour because we talked about the book at my church group," says Charleine Bitter. "I now find myself asking about how much power and control the Pope really has."
The Da Vinci Code has made author Dan Brown a household name
Her son Mike nods.
"I think there are parts of the book you believe, parts you want to believe, and parts you simply can't believe but wonder if its true," he says.
There is no official response from the Vatican to the Dan Brown phenomenon, although one top ranking Cardinal has blasted the Da Vinci Code's version of Church history. Some observers believe Angels and Demons presents a different challenge.
"The Church should pay attention to what's happening here," warns John Allen, Vatican correspondent for the National Catholic Reporter. "Yes, Dan Brown may be inaccurate but he has stirred up incredible curiosity in the way the Vatican works.
"There are two ways for the church to look at this - either as a poisoned pen letter from a secular world that doesn't understand, or as a teaching moment.
"Surely this is an opportunity for them to show they are not an occult force shrouded in mystery."