“JOURNALISTS and police detectives are quite similar, aren’t they? They both dig down below the surface. That’s why the main character in my new book is a journalist who started out at The Argus,” said bestselling crime novelist Peter James as his new standalone thriller Absolute Proof is published.

His protagonist is investigative reporter Ross Hunter, who nearly didn’t answer the phone call that would change his life - and possibly the world - for ever.

The call is from a man who claims he has been given absolute proof of God’s existence and wants the journalist to help him get taken seriously.

Through the stories of the false faith of a billionaire TV evangelist and the life’s work of a famous atheist as well, the book explores the consequences of proving God’s existence, including incurring the wrath of the world’s major religions.

Perhaps the most intriguing part of the story behind his “twisty” plot is the fact that the idea came from Peter’s own personal experience.

“This is a book I have been working on since 1989,” said Peter, the author of the hugely successful Roy Grace series of detective novels as well as standalone novels. “It all began when I got a phone call out of the blue from an elderly man called Harry Nixon, who said he’d been given absolute proof of God’s existence and that he’d been told I was the person to help him get taken seriously.

“I was initially wary but also intrigued and invited him over. I asked him to come at 4pm because my wife was due home at 5.30pm, so if he had me in a stranglehold by that point…

“He looked like a bank manager and took what looked like a 1,000-page manuscript out of an attache case. He said he had been channelled to me by God and wanted me to read the manuscript, which he said contained three sets of coordinates: to the tomb of the Egyptian pharaoh Akhenaten, the Holy Grail and the Arc of the Covenant. He also mentioned Chalice Well, a holy site at Glastonbury, which as legend has it sprang from the ground at the location where the chalice – the Holy Grail – that Jesus drank from at the Last Supper was placed.

“He didn’t want to leave the manuscript with me as it was the only copy but eventually agreed to. It was like Biblical tracts, part badly typed and part badly written, and 20 minutes in, I lost the will to live.”

It wasn’t until a strange coincidence that the author began to rethink his experience. After giving an interview to a radio station, he sat chatting to the producer, who mentioned that her uncle was a trustee of Chalice Well.

“I thought, ‘Clearly I’m the chosen one’,” said Peter, who lives with his wife in a Victorian rectory near Henfield. “I contacted a friend of mine, a bishop, and he said that proof is the enemy of faith and that he would need more than three sets of coordinates as proof.”

While Mr Nixon kept in touch with Peter over the following decade, and indeed the book is dedicated to him, the experience had set in motion a train of thought and 25 years of “the most fascinating research I have ever done”.

“I have always been interested in what happens before we were born and after we die and I started talking about it to anyone in the clergy I could,” said Peter, whose mother was Cornelia James, glovemaker to the Queen. “I spent time in a monastery in Cowfold and five days and nights in a monastery in Greece a few years ago.”

His opportunity to finally write the book came last year after he tore his ankle ligament and was stuck in a foot brace for two and a half months. “I wrote the book in eight weeks,” said Peter. “It was the fastest I’d ever written a novel. But I had already done the research – all I needed was the ‘gosh, wow’ ending and then it came.”

Exploring the subject of Absolute Proof has had “a big impact” on him. “I would describe myself as agnostic/atheist,” he said. “My mother was a Jewish refugee who fled Europe and lost relatives to the gas chambers, so she found it hard to have faith. My father was an Anglican and I was sent to Charterhouse, where we had religion rammed down our throats.

“During the course of the book, I met so many intelligent people who have some kind of faith and I have generally found their arguments more rational than atheists. I’ve talked to all the different faiths and it has been a fantastic journey. The thought that there is intelligence behind the cosmos is overwhelming.”

Absolute Proof by Peter James is published by Pan Macmillan on October 4. The audiobook is read by Hugh Bonneville.

Read exclusive extracts from Absolute Proof in The Argus all this week.

l Peter James will sign copies of Absolute Proof on Thursday, October 4 at:

Sainsburys, West Hove, from 10am-12noon

WH Smith, Churchill Square, Brighton, from 1pm-2.30pm

Tesco, Shoreham, from 3pm-5pm

Waterstones, North Street, Brighton, from 6pm-7pm

and on October 5 at:

Asda Superstore Hollingbury from 10am-11.30am

Tesco Superstore, Lewes, from 12.30pm-2pm

Morrisons, Seaford, from 3pm-5pm.

l The new stage play of The House on Cold Hill by Peter James, starring Cranford actor Joe McFadden, will be at the Theatre Royal Brighton from March 4-9.