nerve centre, goes on sale on February 21, just one week before the pope takes the nearly unprecedented step of quitting as the head of the world's largest church.
Thavis, who covered the Vatican for 30 years until retiring from his post as bureau chief for the U.S.-based Catholic News Service last year, had long known Benedict believed a pope could resign and worried he might do it before the book came out.
But he says he was as shocked as anyone else when the pope announced his decision on Monday. The book is not an analysis of the soon-to-end pontificate, but the stories it tells amount to what Thavis calls "a mosaic history of Benedict's papacy."
Thavis, who came to Rome from Minnesota to promote the book, spoke to Reuters at the Vatican press office.
What does it feel like to have Pope Benedict as your PR agent?
"My friends have all emailed me telling me the pope is my best PR agent. I have to assure them that I did not arrange this. The fact my book is coming out now is perfect timing but it's definitely unplanned. I don't have the gift of prophesy. I worried what effect it might have if the pope were to resign."
Did you have any hint he would resign now?
"I always thought he would resign. He spoke about it in a book two years ago. Then he put the trip to Cuba and Mexico on his agenda and I thought he wouldn't. But when he suddenly named six new cardinals last November, I asked people in Rome if he was thinking about resignation. They didn't seem to be too concerned. But I followed what was and what wasn't on the pope's calendar and by January I was quite concerned. I planned this trip to Rome because I thought February 22 would be a likely time. That's the Feast of the Chair of Saint Peter, which is the feast associated with the authority of the pope."
In the book, you call the Vatican "a kind of showcase for missteps, distractions and mixed messages, a place where the pope is upstaged by his own gaffes or those of his top aides." Did this come out in your daily reporting?
"There were some things I couldn't say until I sat down to write a book. There were some judgements I couldn't have expressed in news stories, and not only because I worked for a Catholic news agency. I couldn't say in my daily reporting how disgraceful I found the Legionaries of Christ's effort to spin or deflect criticism from their founder (Fr Marcial Maciel, who sexually abused boys and secretly fathered several children).
"I also couldn't say how ridiculous I found it that the Vatican still feels the need to edit the pope's spoken words to journalists, as if there was an official version that will supercede his actual words."
Was there one point when you felt you had to write it?
"When we were touring with John Paul II in 1988 in Swaziland, the king arrived for the papal Mass after the pope had started. He came in a convertible Cadillac with two of his four wives and the pope's sermon that day was on polygamy. I said to myself, somebody should be writing this book and maybe it should be me."
Religions can be very complicated, especially a worldwide faith like Catholicism. Does that make it difficult to report on the Vatican?
"Most 'vaticanisti' -- the journalists who cover the Vatican -- feel a real limitation on their reporting. The Vatican is a 2,000 year institution. Most decisions have a history and a back story that often doesn't get told.
"When Pope Benedict said in his book in 2010 that the use of condoms by a prostitute may constitute a step towards moral responsibility, the press more or less treated it as if it fell out of the sky. There was in fact a 10- or 20-year hidden discussion by the Vatican's moral theologians on this very point. That's the kind of context neither I nor most reporters can possibly fit into an 800-word news article."
You argue that poor management in the Vatican leaves individual staffers there a lot of leeway to push their own agendas. How does that work?
"We all tend as reporters to treat the Vatican as a powerful hierarchical institution that knows what it's doing every step along the way. The more you dig, the more you find it is much less organized and less hierarchical than it seems and much more based on individual personalities.
"For example, the process of declaring someone a saint is often driven by personalities who are working very hard behind the scenes. In the case of Pope Pius XII, I think his cause for sainthood has really been driven in large part by a German Jesuit, an American nun and an American Jewish activist - an unlikely triumvirate of people."
Are there other reasons why readers don't hear more of the stories you recount in the book?
"The original title for the book was 'Backstage Vatican.' Much of what happens at the Vatican is, in a sense, theater. The conclave is a classic example. Generally journalists don't go poking around backstage because there's no time, no newshole, not enough space to tell theses stories.
"Even when we write long pieces, we tend to write about policy and analysis, things that don't really get at the day-to-day life at the Vatican and how it works. I wanted to give a glimpse of this backstage reality.
"Because we cover the Vatican fulltime, I actually had the time to go back and ask the man who rang the bells at the conclave in 2005 why they didn't ring right away when the white smoke started coming out of the Sistine Chapel. I was able to tell what it's like to be the monsignor who takes depositions from victims of sexual abuse, or the papal gentleman who escorts kings and queens and presidents to meet the pope and then makes style judgments on them."
You have a whole chapter with stories about the mishaps during John-Paul's globetrotting, the very scripted visits Benedict has made and the antics the journalists get up to. That's another aspect of Vatican life that readers rarely see.
"I realized that, in all my papal travels, no one had written a kind of "boys on the bus" book and I definitely wanted to include at least one chapter like that. Like most people, you come home from the office and your wife asks what happened that day. After you tell her, you realize that what you've just said was a lot more interesting than what you wrote. So I collected the flavor, the personalities, the atmosphere, the humaneness of the place. That's what's missing from most reporting."