DON'T let anyone try telling you Edwin Thomas doesn't do his research.

A year ago the bespectacled, quietly spoken York author found himself high in the Andes. He and a friend were journeying from the ancient Inca capital of Cusco down the flank of the mountains to the headwaters of the Amazon almost 10,000 feet below.

They negotiated a series of sweeping hairpins through the cloud forest that clung to the mountainsides. Ahead dizzying views would open up of valley after valley draped in cloud.

And then, suddenly, the road ran out. There had been a landslide, and the road had literally been washed away.

Extraordinarily, there was a team of Peruvian construction workers doing repairs, says Edwin, 38, a married dad of two from Dringhouses who writes under the pen-name Tom Harper. "There was a digger balanced on a tiny fragment of surviving road, looking like it would fall into the chasm."

York Press:

Cloud forests on the flanks of the Andes

Edwin and his friend Kevin were stuck for two hours, while the workmen built a section of stone road just wide enough for their truck. And then they had to drive across...

The pair's journey was really only just beginning. They reached the base of the Andes, more than 9,000 feet lower than where they had started. The air was hot and steamy, the jungle thick. "We came around a corner, there was a wall of cloud - and then the start of the Amazon," Edwin recalls.

Edwin - who, as Tom Harper, has written a string of bestselling adventure novels such as Zodiac Station, set in the Arctic, and The Orpheus Descent, set in both ancient and modern Greece - was researching his new novel, Black River.

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It is the story of a group of treasure hunters who venture far up the Amazon in search of the fabled lost Inca city of Paititi, said to lie hidden in emote rainforests at the foot of the Andes.

Edwin decided his book wouldn't be authentic if he hadn't travelled there himself.

He hired a local guide, Fernando Rivera, over the internet. And when he and Kevin completed their drive down the flanks of the Andes to the headwaters of the Amazon they continued their journey, with Fernando and a local Indian named Callixto as their guides - this time heading up a tributary of the Amazon in a boat known as a peque-peque. Eventually, the water became so shallow even their boat couldn't go any further. And so the party set out on foot...

York Press:

Kevin, Fernando, Callixto and boatman Roberto on board a peque-peque. Photo: Edwin Thomas

They were heading for the Pusharo Petraglyphs, a series of mysterious rock carvings etched into the face of cliffs deep in a remote area of the Peruvian jungle.

"They're carved with mysterious symbols," Edwin says. "Nobody knows who made them or what they are. As far as I know, nobody has ever managed to date them." But the legend is that they point the way to Paititi, he says.

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The Pusharo Petraglyphs

It is a city said to have been built by the last of the Incas after their great empire was brought down by Spanish conquistadores 500 years ago. The last surviving Incas fled into the Amazon jungle with their treasures, and built a great stone city, goes the legend.

There are still treasure hunters who search for the lost city and the lost Inca treasure it is said to hide to this day.

Edwin and Kevin spent ten days in Peru, part of that time spent hacking through the remote jungle in the footsteps of their guides as they approached the ancient rock carvings that supposedly show the way to Paititi.

It was hot and humid, the jungle alive with insects - among them tiny red flies that settled in thick clusters over their sweat-soaked bodies. At night they'd stay in native lodges, while Fernando told stories of the treasure-hunters who had gone before them: an American dentist; a Spanish policeman; a French civil servant - all men obsessed with the idea of finding the lost city.

York Press:

Edwin Thomas, left, Fernando Rivera and Callixto, a local Matsiguenka Indian guide, hack their way through the Amazon jungle

Edwin never found Paititi, of course - though he did get to the petroglyphs, something only a dozen or so travellers manage each year because they're so remote, he says proudly.

A husband and father, he was on a tight timescale, and home was beckoning.

But he returned with a head full of tales of treasure hunters and lost cities, and a first hand knowledge of the jungle, that he has put to good use in his new novel.

Black River tells the story of a group of treasure hunters, among them a London doctor suffering a mid-life crisis, who do go seeking the lost city of Paititi - and who find it.

That, however, is only the beginning of their troubles. In a way, Edwin's novel is a version of the classic Humphrey Bogart film The Treasure of the Sierra Madre, in which three gold prospectors go in search of gold - and when they find it, turn on each-other full of suspicion and hatred.

Does something similar happen in Black River?

That would be telling, Edwin says. "But they find something. The book is about what happens then..."

And what about Edwin himself? Would he be tempted to go back to Peru to resume the search for Paititi?

Quite possibly, he says. There's something about those tales that grabs at you.

When he and Kevin were trekking through the jungle with Fernando, they were forced to stop by a torrential rainstorm.

Fernando whiled away the time telling them stories.

"And if somebody had turned up then and said 'I'm going looking for Paititi, are you coming?' - well, we just might have gone with him."

Just don't tell his family...

BLOB Black River by Tom Harper is published by Hodder & Stoughton, priced £19.99