As unseasonable October sunshine streams through a window high in Covent Garden, Robert Harris, the genial and welcoming author of Conclave, has every reason to be happy.

His new book is a thriller set in the enclosed world of a fictional conclave. All the action takes place in the Sistine Chapel and the Domus Sanctae Marthae, the cardinals’ residence, or between the two. There are none of the usual set pieces common to thrillers, such as chases or discoveries of mangled corpses, though there is some broken crockery and, at one crucial point, some noises off. Yet the tension of the story, delivered through the unities of time and place, keeps the pages turning briskly. Who will be elected? Which candidate will break from the pack and make it past the two thirds needed? There’s nothing to see, except a group of old men voting, but it’s the greatest show on earth.

How political is the Catholic Church, I ask Harris? Is the Catholic Church pretty much like New Labour, which he knew well as a prominent early supporter of Tony Blair? He replies that the whole point of the novel is that there is a difference between the Church and the secular world. A conclave is not to be confused with what might go on in a secular organisation. There are, of course, rules to a conclave, but they govern a spiritual reality. To see the workings of the conclave from the outside would be a terrible mistake, but fiction allows you to get an inside view.

“I approached the book with a certain trepidation,” he says, “because I recognised that if you didn’t – and I am speaking as an outsider obviously – that if you treated the Vatican simply as if it were ICI or a secular organisation, you would miss the point.”

The inside view is provided by his leading character – and, in many senses, his hero – Cardinal Lomeli, the dean of the Sacred College. The reader sees the workings of the conclave from his perspective: that of a tired old man trying to keep the show on the road, and, at the same time, a man of faith and prayer, though constantly plagued by doubts. It’s a religious perspective, not, as Harris puts it, the Dawkins view, which would be worthless.

At the mention of the celebrity atheist, I ask the inevitable question. Does Harris believe in God? I get the impression that this is a question that does not often come up. “I dislike easy atheism,” he says. “I think atheism is an easy route, a boring route, to take. I am rather drawn to people who take the more difficult route and try to engage with a greater thing. I have empathy with that.

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