You wrote The Rise of Benedict XVI in two weeks. How?

It took less than two weeks. I started April 26 and finished May 7. I need to get away and focus to write a book. I told my wife, "We can go anyplace in the world you want, because I'm not leaving the hotel room." So we went to Paris for a couple of weeks and I stayed at the keyboard for 16 hours a day.

You mention that John Paul II had a reputation as a poor administrator. Is that true?

John Paul's focus was, to use a Latin phrase, ad extra, meaning outside the church. His passion was a dialogue with the world and other religions. He focused on ad extra issues and left the Church administration to others.

Such as Cardinal Ratzinger, now Pope Benedict?

Yes. Virtually all of the important theological decisions of the Catholic Church in the last 24 years were largely made by Cardinal Ratzinger. In many ways he was the intellectual architect of John Paul's papacy.

You write that the impact of John Paul's funeral and the attention it garnered helped Cardinal Ratzinger get elected. How?

Prior to the conclave there was the idea of finding a quiet transitional pope—someone who could allow the church to catch its breath after the papacy of John Paul—but not a visionary, world-class figure. But the "funeral effect" made that impossible because the cardinals realized that if they did not elect someone of true substance, then whoever they picked would be crushed by the comparison with John Paul. They needed someone to stand on the world stage and impress people with his vision and intelligence. And as they looked around the college, it was a relatively short list.

So despite the hoopla in the media, it wasn't a very close race after all.

Correct. The list of cardinals who have the constellation of qualities I mentioned—intellect, vision, linguistic skills—is fairly short. Others were eliminated for various reasons—Italy's Cardinal Carlo Maria Martini because he has Parkinson's disease, or Chicago's Cardinal Francis George because he's an American.

You have a book coming out from Doubleday this fall on the conservative Catholic group Opus Dei, which thanks to The Da Vinci Codehas a mysterious reputation. What is your book about?

The book is an attempt to separate fact from fiction about Opus Dei and take all the popular images of [the morganization]—the secrecy, the money, the power, the recruiting, the role of women—and establish how much is true and how much is false. I had complete access to their archives, their finances and their key decision makers.