The hamlet of Clearbrook offers breathtaking views of Dartmoor and very little else. Shortly before you reach the lone pub, behind a row of whitewashed houses, a narrow pathway leads to a tiny stone cottage. It is here that I find Camilla Carr and Jon James, an ostensibly unexceptional couple with an extraordinary story to tell.

Look at photographs of them and they may appear vaguely familiar. Eleven years ago, for the worst of reasons, they became a cause célèbre when, while working for a children's charity in Chechnya, they were kidnapped. Their captors placed a £1 million ransom demand on their heads and, amid brief interludes of compassion, subjected them to beatings and told them they would be tortured and shot if they didn't admit to being spies.

Camilla was raped repeatedly and Jon had to endure a mock execution with a cocked gun held to his chest. For more than 14 months they were locked in cellars and sealed rooms with no daylight, and often with no electricity or even basic sanitary provision. Their eventual freedom came about in a pre-dawn raid orchestrated by the billionaire Russian oligarch Boris Berezovsky that would not be out of place in a Bond movie. When, in September 1998, they flew into RAF Brize Norton in Berezovsky's private jet, they appeared, at first, to be remarkably unscathed. But behind the scenes, euphoria quickly gave way to what Jon calls champagne cork syndrome. “You come out from under the wires, fly high, and then bump, bump. Depression. Collapse.”

It has, they concede, taken a decade to absorb the shock, anger and grief of being held on a constant knife edge. This week, they publish the full, riveting account of their ordeal and its aftermath. The Sky is Always There tells, with unsparing honesty, how they endured, why they forgave their kidnappers and what strength they drew from each other. It exposes their naivety, but ultimately it offers the hope that, even in the most extreme adversity, the human instinct for survival is indefatigable.

The first thing that strikes you about Camilla and Jon is that they are not, on the surface, the most likely of couples. At 47, he is a former bricklayer who grew up in Gloucestershire, the son of a postman. She is the daughter of an Old Etonian father and a mother who is the descendant of an Indian princess. They met in 1994 at a swimming pool in Ross-on-Wye. Each of them had a son from previous relationships, but for complex reasons that emerge as their story unfolds, neither of them were hands-on parents. They shared a passion for yoga and t'ai chi, and there was also an instant chemistry between them. Jon remembers it as a “huge vibe - a magnetic pull”.

They had been seeing each other for just over a year when, during a chance meeting in a café, a friend told them about his plans for a children's centre in the Chechen capital and asked if they would go and help to set it up. The Russian onslaught on the breakaway republic had taken place two years earlier, and the country remained war-ravaged and extremely dangerous. They were warned that anyone going there risked kidnap, and yet, Camilla says: “I felt it was our destiny. We were following our hearts, not our heads.” When they describe their 2,000-mile journey from Gloucester to Grozny in a £500 Lada laden with paints, toys and footballs, you can but gasp at their treacherous innocence.

They were kidnapped within two months of their arrival. Masked men carrying Kalashnikovs burst into their house on the outskirts of the city in the early hours and took them, handcuffed and blindfolded, to a building where they were shoved through a trapdoor into a dank cellar - the first of 14 prisons that they would occupy in the ensuing 443 days.

In the book, they describe vividly their fluctuating mental state as the reality of their predicament hit home. They knew instinctively that their only way to survive was to build up a rapport with their four main captors. Using a Russian/English dictionary, they listened to stories of how the war had blighted their lives - one, a former car dealer, told how his wife, brother and father had been killed, leaving his elderly mother to look after four orphaned grandchildren - and how they were having to resort to kidnapping as a form of income.

When stoned on marijuana, which was much of the time, the kidnappers would become aggressive and violent. To alleviate their guilt at carrying out the kidnap without justifiable reason, they started accusing Jon and Camilla of working for Mossad or the CIA. Brandishing a large kitchen knife and a small digital clock, they told Jon that he had half an hour to tell the truth before they cut off his fingers. Another time, they pushed his back against the wall, pointed a Kalashnikov at his chest and drew back the bolt. “I thought then that I was going to die,” Jon says. “But I also felt incredibly calm. I was powerless, and when you realise that you surrender - there is nothing else you can do.” Camilla recalls: “My heart was in my mouth. I was watching their eyes through their masks, trying to work out whether it was for real or a sick joke, and then the gun jammed, and they all burst out laughing.”

The vilest moments were the rapes of Camilla, carried out by the guard they nicknamed Paunch. When in sole charge, Paunch would take Jon at knifepoint, chain him to a radiator and then drag Camilla into another room. Afterwards, he would insist that Jon played him at backgammon. The “ritual” was repeated more times that they could count. For Jon, the worst “was knowing each time, what was to come”. Camilla says she got through it by telling herself “You can never touch the essence of me. My body is only part of who I am.” Much later, Paunch apologised to her, explaining that he had thought, because she was a Western woman, that she “would not mind” enforced sex.

Their living conditions varied from barely habitable underground cells to a place they called the pink crystal room - a large, high-ceilinged space with a polished parquet floor and startling cerise bedspreads. They went weeks at a time without hot water, savoured the fresh food when it was offered, and subsided on watery soup and stale bread when they had to. Towards the end of their captiv- ity, they were forced to share a concrete box 9ft 6in by 12ft 6in with another prisoner, who, it transpired, had been a special envoy for Boris Yeltsin. “Until he arrived, we hadn't realised how much we had slowed down,” says Camilla. “He finished his meals before we had barely eaten two mouthfuls.” With nothing to read, and no diversions, food had become a highlight of their day. They used meditation and yoga to fill the hours and to soothe frustration and anxiety.

Remarkably, they never argued. “The closest we came to a fallout was when Camilla thought that my rice pudding was bigger than hers. I shoved the bowl in front of her and said: ‘There you go. Eat it',” says Jon. They smile wryly at the memory. “The thing is, we don't argue. Never have,” says Camilla.

They had no idea they were to be freed until the night a guard told them “Demoi!” (“Going home”) and bundled them into a car. When another guard removed the blindfolds that had been placed over their eyes, they looked up to see the sky for the first time in more than six months. An hour later, they were across the border into Ingushetia. There they were taken to a five-star hotel room full of large, Russian-speaking men surrounded by half-empty bottles of wine and vodka. After a bath to soak away of layers of grime, they travelled in a cavalcade, sirens blaring, to an airport swarming with armed police, and on to Moscow, where Berezovsky joined them with his entourage, shook their hands and offered his private jet for their onward journey.

They have never known whether money was exchanged for their freedom, or who their captors were. Although they were initially curious, their need to reacclimatise soon became the overriding priority. Camilla remembers feeling immensely calm and grounded as they were reunited with their families. It took many months, however, for them to adjust to the speed of normal life. “Just listening to people talk across each other was exhausting,” says Camilla. “We had been so used to silence, or conversations where you waited for the other person to stop talking before you started.” After such an intense time together, they had to adjust, too, to being apart. “We had shared our life stories, our deepest thoughts, but Jon had a lot of suppressed anger afterwards and I didn't have the energy to help him.”

When, months after their release, he disappeared for two days, she feared that he might kill himself. “It was a very tough time, but I just had to trust that he would find a way through.” He had, in fact, gone to London, where he wandered the streets all night while his mind erupted in confusion and turmoil. “Camilla and I had relied so much on each other, but we had got to the point of saturation, and I couldn't ask her to help me.”

Jon had proposed to Camilla while they were in captivity and their wedding, a year after they came home, was a joyful occasion. But there have been darker moments. Camilla has had cancer diagnosed twice - first a melanoma and then a stomach tumour. “I'm good at ‘holding on', but the tension has to find an expression, and in my case, intuition tells me it came out as cancer,” she says. She is now through treatment, but “I have to be careful with my nerves”. In the two hours that we have spent talking, it is clear that, although she exudes poise, she is more vulnerable than she looks.

A big part of their catch-up time was spent with their sons. Jon's son Ben had lived with Jon's parents since he was two years old. Jon had been just 19 when he was born. He had married Ben's mother, but she later left them both, saying that if she stayed she would have a nervous breakdown. During his time in Chechnya, Jon missed Ben's 18th birthday. On his return, there was, he says, lots of “talking through our anger, crying our tears and hugging each other.”

For Camilla, the long, empty hours in Chechnya gave her time to contemplate the decision that had reverberated throughout her life. Her son Ashok was born when she was 28. She and his father Marcel, a Dutchman, were together for five years before Marcel left her for another woman. In her desperately low state, Camilla had agreed that Ashok should live with his father. Marcel had taken Ashok back to the Netherlands and although she visited regularly, Camilla now acknowledges that she made a huge sacrifice. “I had lost my motherhood,” she says. “I wasn't there to help him brush his teeth, to help him if he fell over. I remember arriving to see them early one morning just as Ashok was going off to school and it was crippling, because it brought home to me how I was no longer part of his daily life.”

In the book, she writes about her sense of failure as a mother. “That failure lurked in my subconscious for years,” she says. “I don't think I even managed to voice it until I came to write about it.” For both Camilla and Jon, the unquenched need to nurture explains much about their eagerness to work with the war-traumatised children of Chechnya.

Ben is now 28 and living with a girlfriend in Sheffield. Ashok, now 22, came to Devon when he was 18 to be close to Camilla, but has since gone travelling. How would they feel if either of them wanted to do voluntary work in a war zone? “We wouldn't dissuade them,” says Camilla. “They've both seen it from the other side, so they know the risks.”

In a material sense, Jon and Camilla areworse off than they were before they went to Chechnya. They lived and worked at a yoga centre in Wales before coming to Dartmoor two years ago to be nearer to Camilla's mother. Jon is an odd-job man and part-time tree surgeon. Camilla gives talks to schools about “survivorship”, is training to be a drama therapist and also works as a cook and cleaner. Their cottage is rented and smaller than some of the prisons in which they were held. Their worldly possessions amount to a second-hand sofa, a 30-year-old gas stove, a recycled laptop and a battered car. But they savour the freedom to step out of the door and on to the wild and expansive moor. Ask them what they cherish most, and they answer in unison: “Fresh air”.

Their captivity stole 14 months of their lives, but they bear no resentment now towards their kidnappers. Camilla even forgave the man who raped her. “It helps when you understand where the person who harmed you is coming from,” she says.

Nor do they have any regrets. They went to Chechnya as two lost souls and returned with their relationship cemented. “We saw each other stripped to the core, and that bonded us,” says Jon. “Although not in a rigid way,” adds Camilla, reaching across their rickety kitchen table to stroke his arm.

The Sky is Always There: Surviving a Kidnapping in Chechnya by Camilla Carr and Jonathan James, Canterbury Press, £14.99, is published on Thursday

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