Jean-Christophe Lafaille was the most gifted mountaineer of his generation. Small, strong and fearless, he ascended the world's highest peaks without oxygen or back-up; climbing alone because no one else could match his supernatural speed. Then, three months ago, with the 8,000m pinnacle of Makalu in his sights, he vanished. Jason Burke his final steps

On his last morning alive, Jean-Christophe Lafaille woke up perhaps the most profoundly alone man on the planet. His tiny tent, specially designed for ultra-high altitude, was perched on a small ridge at around 25,000ft on an icy shoulder of Makalu, the world's fifth largest mountain. Either side of the tent, huge rock and snow cliffs and avalanching slopes swept down to the distant valleys of the high Nepalese Himalayas. There was nothing above him except Makalu's summit, some 3,000ft higher.

Lafaille had slept through his alarm and woken around 5am, when he called his wife Katia to tell her he was now up and moving. Ahead of him was a day that few normal human beings could have survived for more than a few minutes. Even by the standards of this most gifted and hardened mountaineer, the task Lafaille had set himself was almost unprecedented in modern mountaineering. Outside it was around -30C, still dark, with a light wind. The summit of Makalu would take 10 hours of hard and dangerous climbing to reach; up steep ice slopes, through crevasse-strewn glaciers and rocky cliffs, gasping in the thin air at an altitude at which passenger jets cruise. No one had ever climbed the mountain in winter before - let alone without oxygen, or back-up. Lafaille made himself a hot drink, ate a little, stuffed food and water in his rucksack, pulled on his boots and picked up his ice axes. Before leaving his tent, he rang his wife again. And then the finest climber in France, arguably in the world, disappeared.

It was late January this year and Lafaille, 40, was climbing in the hardest way possible. He had no rope mates, no porters, no rescue team. At his base camp, 7,000ft below, there were three local Nepali sherpas with a radio. There were no other expeditions anywhere near him, and no one else on the mountain. Lafaille, as he always preferred, had the huge expanse of rock and snow and ice, and the cold and the wind and the great arcing vault of the Himalayan sky all to himself. His only link to the rest of mankind was a portable satellite telephone - which he had been using to call Katia and his four-year-old son several times a day.

This is a story of love and death, of the complex and often difficult relationship that a prodigiously gifted, driven man such as Lafaille can have with a sport - a sport which for him was a profession, a vocation and a passion. It is a tale of his extraordinary relationship, framed by the world's highest and most dangerous peaks, with his wife, lover, closest friend, professional partner and the mother of his child. This is the story of the short, happy life of Jean-Christophe Lafaille.

Lafaille was born in Gap, in the foothills of the French Alps, in 1965. He started climbing at a young age, inspired by the books collected by his father, a keen amateur mountaineer. He quickly proved to be an extraordinary talent, forcing new and spectacular routes on the rock cliffs near his home. Such exploits were not particularly dangerous - climbers protected themselves with a system of metal bolts set into the rock - but they were extremely demanding. Lafaille's compact 5ft 3in, 8st 6lb frame did not hold him back. He was not very interested in drinking and going to nightclubs as a teenager, he said later, almost apologetically.

Soon, he graduated to the high mountains of the Alps, where he quickly proved himself. The fiercely competitive French mountaineering milieu began to take notice when the young upstart climber began 'repeating' some of the hardest routes in the Mont Blanc massif. Such routes sometimes took days, though Lafaille cracked them with an extraordinary speed and technical proficiency that was to become his trademark. Lafaille first climbed the hardest existing routes and then spearheaded a new wave. The climbs took him into a vertical universe where, under constant threat of rockfall or avalanche, he climbed overhanging ice with axes and crampons, and scaled walls of rock using metal pegs only slightly thicker than a coin, hammered into minuscule cracks as holds. Many climbs he did alone, setting up complicated rope arrangements to protect himself or merely relying on his own ability to avoid a fall of several thousand feet.

In 1992, one of France's top mountaineers, Pierre Beghin, asked Lafaille if he would like to go to the Himalayas to attempt a complicated and extremely challenging new route on Annapurna, one of the 14 peaks in the world that are more than 8,000 metres (26,000ft) high. He was 27 years old and could only accept.

The trip went horribly wrong. After several days of climbing, high on a huge, exposed face of Annapurna, a mountain almost double the height of Mont Blanc, a storm erupted and the two men decided to descend. To climb down a vertical wall of complex terrain the size of Annapurna is as dangerous as climbing up, if not worse. The two men began to abseil, fixing their 150ft-long rope to spikes of rock or lumps of ice, then sliding down it, before pulling the rope down and using it again to descend a little further. Occasionally, when nothing else was available, they used metal pegs or a piece of equipment known as a 'friend', which expands and takes a hold in cracks when weighted, to fix the rope to the mountain face. But such devices are not foolproof. Beghin fixed a 'friend' and had just began to abseil when the artificial anchor popped out. Lafaille was watching his far more experienced rope mate from above, and looking straight into his face, when the rope slipped and Beghin fell backwards into space. Any fall at that altitude is usually fatal. Beghin, carrying the bulk of the two men's equipment, dropped the entire length of the face.

Lafaille was left alone, with no food, no water and almost no equipment, and with an arm broken by rock fall. It took him five days to climb down the vertical mile or more of rock and ice to base camp. Lafaille later described looking out from the wall as he descended and seeing the lights of the trekking lodges in the valley below, a world of security and comfort and human warmth that seemed impossibly distant. Pictures taken of the young mountaineer after the ordeal show him almost destroyed, a terrible hunted look in his hollowed eyes. Yet he did not give up climbing.

I know Chamonix well, but I still stop the car when I round the bend in the steep road and the vast white wall of Mont Blanc swings into sight at the end of the valley. It is, as ever, a breathtaking sight. I can see the ridge at 14,000ft where I once bivouacked, 15 years ago, ill-clad in borrowed clothes. To the young Lafaille, Mont Blanc was a testing ground and a playground. He would have seen the possibilities of purer and purer routes, each taking the most natural, the hardest, the most direct line to a summit. He would also have read - as commuters read newspapers or traffic reports and farmers read fields - snow conditions, rockfall danger and the weather.

I have come to Chamonix to interview people who knew Lafaille. Everybody knew him in a way: as France's best-known climber his face adorned the covers of dozens of magazines. Climbers in France are major celebrities, household names, almost pin-ups; their exploits are major news stories. France even has a minister for mountaineering. The reasons for this interest are manifold: the Alps, the Pyrenees and the sun-drenched crags of the south of the country are all an integral part of the image the French have of their own country, as important as cheese or wine. The men and women who perform such extraordinary feats among these mountains represent something in the national spirit. It is no surprise to see Lafaille's sharp, elfin features on posters in half the outdoor gear shops in the country.

A number of journalists - many of them climbers - have told me how, after the Annapurna tragedy, Lafaille went on through the mid-Nineties to push back the barriers of modern mountaineering further and further. Not content with simply climbing the great north faces of the Alps individually, he did nine of them, including the famous Eiger, one after another without pause in 15 days, skiing from one to the next. When his work as a guide and instructor in Chamonix allowed, he returned to the Himalayas to complete a series of difficult new routes. Instead of climbing with huge expeditions, with ropes fixed to allow easy ascent and escape, and porters carrying tonnes of equipment, Lafaille often climbed alone, almost always without any support, and certainly without any oxygen. All the journalists who had interviewed Lafaille described him as eerily quiet, modest, unassuming, friendly and gentle. 'Very different,' said one, 'from your average screwed up, egomaniac, hyper-sensitive top-flight French climber, or any ultra-high level athlete for that matter.'

But though many reporters praised Lafaille, they did not all rush to praise his wife, Katia. I had expected Lafaille to be the classic driven climber who leaves his wife and family to single-mindedly pursue a selfish and irresponsible dream. But the critics told another story: Katia cut him off from his friends and turned him into a media star. One went further. On Makalu, the final climb, it was the media pressure that eventually pushed him too far, he said. His wife was in charge of the media ... draw your own conclusions, he implied. Harsh words indeed about a widow, I thought, but wrote them down nonetheless.

Yann Geizendanner is Chamonix's Mr Weather. He has worked at the local meteorological office for 30 years and is consulted by many of France's top climbers. He began working with Lafaille eight years ago, not for money, but for the sheer joy of helping an extraordinary climber enter the history books.

We meet in his flat on the slopes above the town. Through the kitchen window I watch the thick clouds coiling around the Bossons glacier, a mile-wide jumble of vast ice-blocks - seracs - and crevasses; gaping splits in the ice that could swallow a house. The clouds descend as the light goes out of the sky and night falls. 'Who was Lafaille?' I ask Geizendanner.

'There was Lafaille,' he says, 'but there was also the Lafaille couple. If Katia had not existed Jean-Christophe could never have been able to do what he did. It was a combination unique in the mountaineering world. It was thanks to the money she was able to bring in that he could climb like he did. We were a team,' he explains. 'Katia handled the media, the commercial side and the logistics, I did the weather and Jean-Christophe trained and climbed.'

This is not, I think, the image the critics have sketched. Nor is it the norm in the slightly bizarre world of professional climbing. It is not often you find a top-flight mountaineer with anything that resembles a settled and happy private life. The travel, the drive, the ambition, the danger, the fact that even the most successful climbers do not make a great deal of money, all conspire to make profound relationships in the world of climbing rare. And there are even fewer mountaineers who, like Lafaille, have children and, for good or bad, a partner who is an integral part of their career.

Geizendanner was as close to Lafaille as anybody, other than Katia. After all, Lafaille's life depended on his judgment several times. The most astonishing example of Geizendanner's worth came on the most important mountain of all for Lafaille. In 2002, he and a team of four climbers, all of them among the best in the world, attempted an astonishingly audacious new route on Annapurna. Two turned back, but Lafaille and a partner, trusting a forecast from Geizendanner, pressed on. For five days they climbed along a knife-edge ridge from which the slightest wind or mistake would send them plummeting to their deaths. There was no way they could have been rescued. But Geizendanner's forecast was correct, their strength held out and Lafaille reached the summit of Annapurna. He sat with his legs dangling over the face he had down-climbed alone 10 years earlier, after Beghin's fall, and wept for the man who had died there. It was one of the most incredible climbs of modern mountaineering.

Why did Lafaille climb? I ask Geizendanner.

'He told me that at altitude he would feel independent, autonomous. He would feel his survival instincts alive. He used to say that it was a pleasure for him to be up there. But more and more he liked to be in Vallorcines with Katia and the kids. He had nothing left to prove - to himself or anyone else.

Why did he climb alone?

'Because there was no one as fast or as strong as him,' says Geizendanner. 'Anyone else would have held him back - and in the mountains moving fast is safest.'

What about the supposed media pressure?

Geizendanner shakes his head. 'There was no media pressure. Katia knew exactly what she was doing. She was careful to protect him. In fact, she might have gone too far the other way. The problem was that JC became a bit isolated from his old friends and colleagues. Katia wanted him to focus on training, to not be distracted or worried by the groupies, the criticism, the jealousy. She was the only one to whom he would really listen. Alone, Katia would have done nothing; alone, JC would have been a good alpinist. But together they became a legend.'

How many of the climbers you know are dead? I ask. 'Quite a lot,' Geizendanner replies. 'But they were not madmen or crazies. They didn't have death wishes. It was the need to be up high, and to prove something. And, of course, they did it to earn a living. If Lafaille had been the first Frenchman to climb all 14 of the world's 8,000m peaks he and his family could have lived off it for the rest of his life.'

Seven years ago, in the last serious climbing I did, I climbed to over 7,000m on a mountain in the Himalayas. At that altitude, every step was an enormous effort, and was followed by great rasping breaths. My brain, starved of oxygen, took ages to cope with the easiest tasks. It took me 20 minutes to put on my double-layered ice boots, dully wondering what the L and the R I had marked on them meant. I had no appetite (eating just granola bars or dried fruit, despite the intense physical effort) but a desperate thirst - the need to irrigate my lungs and to offset my altitude-thickened blood. Melting snow for lukewarm soup or tea took hours. I slept in five or 10-minute apnoea-ridden snatches, awakening each time panting like a dog dying in the dark. And then there was the cold. Lafaille plunged his hands and feet into buckets of ice cubes to prepare them for freezing temperatures before his climb. I didn't. I woke with ice on my eyelids. The cold was intense enough to become a nauseating physical pain, the kind you feel when you bark your shins against a low table. When three climbers on another expedition died after making an elementary error of navigation in a fog a few hundred metres from our top camp, I decided to turn back. I have barely climbed since. I was at around 7,000 metres for a day or so on an easy mountain. Lafaille spent weeks of his life at altitudes much higher, often climbing extraordinarily difficult terrain that most experienced mountaineers would not be capable of even at oxygen-rich lower altitudes.

It is difficult to give an impression of quite how fit and mentally strong someone like Lafaille has to be. Ed Viesturs, the first American climber to scale all the world's 8,000m peaks, was one of the few mountaineers with whom Lafaille was prepared to share a rope. Viesturs, a lean and laconic 44-year-old, was one of those who turned back on Annapurna in 2002 when the French climber went on to complete his extraordinary high-altitude high-wire act on his ascent of the mountain.

'I thought it too risky to continue, but JC went on and succeeded,' he says. 'It's a very personal thing. There's no right and no wrong. He was a little guy but phenomenally strong, very, very fast and absolutely gifted. He was technically the most talented all-round climber in the world. He could climb anything.'

After the expedition, Viesturs and Lafaille became close friends, climbing together the following year on two other major 8,000m peaks in Pakistan, Broad Peak and Nanga Parbat. Even though the two men barely shared a common language, Viesturs said they 'could always communicate. He had similar values. He loved his family as well as climbing. I like being with my wife, my three kids, my home here in Seattle.'

I ask Viesturs, who has been on more than 30 expeditions, how he reconciles a family life and his career. 'I have always been a professional climber,' he says. 'My wife knew what she was getting into and I have always told her that I would be as safe and as conservative as I can be. You can manage a risk. A lot of people cause their own problems. They disregard the conditions and go for the top. The art of mountaineering is walking away. Crevasses don't care if you are famous.'

Viesturs rarely climbs alone, but did so on Everest (which he has climbed six times) in 1993. 'It was a psychological journey,' he tells me. 'It's tough, you have nobody to talk to, but uplifting, too. There are not many places on this planet where you can be so alone.'

We talk a little more - about the bitchiness of the Chamonix climbing scene, about how Lafaille was something of an outsider there and about those who accuse mountaineers, especially those with wives and children, of being selfish, egotistic, irresponsible.

'People who criticise are ignorant or stupid. They should go out and climb fourteen 8,000m peaks and then we'll talk.'

Lafaille lived in Vallorcines, a small village set high above Chamonix. To reach it, I drive out of the town, along the base of a valley flanked by huge mountains. It is a dozen degrees below zero. The clouds have cleared and the sky is a crystalline clear blue. A thin plume of cloud is being driven off the summit of Mont Blanc.

Katia Lafaille is 36, small, slim, lightly tanned and strikingly pretty. We shake hands and I say, 'How are you?' and, as people do after a bereavement, she says, 'Fine, thanks' automatically. And then adds, 'Well ... not really fine at all' and leads me into the old school house that she and her husband were in the process of converting into a family home when he set off for Makalu three months before. We walk through a storeroom packed with the blue plastic drums used by climbers to transport equipment. There is a set of skis next to the door.

Katia and Lafaille knew each other for several years before they got together; she was a climber, too, her boyfriends were climbers. 'We were just friends,' she says, 'but there was always a good feeling. We finally got together on New Year's Day 1998. It was a very powerful, very profound love.' She recalls how, 'His eyes sparkled when he spoke about the hills. Other climbers I knew just tried to prove things, to deal with their own issues through climbing; but he just loved their beauty, their purity, being among them, he loved the people who lived among them.'

I ask why Lafaille climbed alone. Katia's answer is different from those of Geizendanner and Viesturs. 'Because he did not want to see another climbing partner get killed like on Annapurna,' she said. 'He preferred to be completely autonomous.' But like Geizendanner, Katia stresses, too, that such autonomy also meant safety. There was no one else, less talented, weaker, to endanger him.

Quite early on in their relationship, Katia, who had worked in PR, took over the commercial side of things. 'Before, Jean-Christophe was just interested in earning a bit of cash to keep climbing. He negotiated his sponsorship contracts with a quick conversation over a coffee. He was an artist, not interested in material things.'

One of the criticisms levelled at Katia was that she had encouraged Lafaille to try and 'tick off' the world's 8,000m peaks. Mountaineering purists often sneer at the 'commercial gimmickry' of the list. Such criticism conceals two very harsh charges levelled against Katia. The first is that Lafaille was 'ticking the list' for sordid financial reasons. The second is that if he had not been ticking the list - he had done 11 of the 14 '8,000-ers' - he might not have been on Makalu, and therefore might still be alive.

'Yes,' Katia says, 'I suggested doing the 8,000m peaks. He said he did not want to get involved in a list, but I pointed out that each year he kept setting off to do another 8,000m peak so he was up on these mountains anyway. I tried convincing him to climb smaller peaks, but he said there was something special on the bigger ones. He loved being up there alone, with the beauty and the emptiness and just him, his strength and skill. So I thought, "OK, if you are going to do it anyway, we might as well do it properly," get everything organised and get enough sponsorship so that he could climb with everything he needed.'

The point is quite simple and silences all the criticism. Yes, Katia made sure Lafaille did what brought in the cash. But she did it so her husband would be safer.

I tell Katia that I had heard that her husband was getting tired of the big mountains. 'To an extent,' she says. 'When Ed [Viesturs] finished his 8,000-ers, Jean-Christophe said that he wished he had finished his. I said: "Fine. Stop then. Stop if you want to." But then he said that he was just interested in Makalu as a project. He said he wanted to do it anyway. It was, in all simplicity, just what he loved to do.'

And in her view, even the attempt on Makalu was very much feasible.

'He originally wanted to do a new route. I said, "A new route? In winter? Alone? No way." And he agreed and switched to a route that has been climbed many times before.'

I think of something Geizendanner had said, about it being 'the couple Lafaille' who climbed. When he was high on the mountain, Lafaille used a small Thuraya satellite phone - it meant that he and Katia talked incessantly. 'Katia was in his head as he climbed,' Geizendanner had said. 'They almost climbed together. She could tell exactly how he was feeling from his voice, how strong he was.' During the climbs, Katia counselled and coached him. She motivated him when he was exhausted and, on several occasions, she got him to retreat when he wanted to go on. On others, such as on the famous ridge at Annapurna, she was at the base camp of the mountain, and she kept him going.

'We were living a love that was extremely strong,' Katia says. 'And he told me: "I have a dream life, I have a wonderful wife, a wonderful son, and I do what I love to do." We complemented each other perfectly. He spent two months a year away on expeditions, but other than that he was at home or with us. We grew an enormous amount together. We had so many adventures to live, but we lived something that, if you are lucky, you know once in your life ... and at least now I have known it.'

We are sitting at the kitchen table. There are children's drawings on the fridge. Lafaille and his four-year-old son Tom, were, Katia tells me - for the first time having trouble talking - extremely close. I am suddenly aware of how raw all this must be. Lafaille died only six weeks earlier. 'It's hard for the little one,' she is saying. 'He says, "Where's Dad got to?"' When there's bad weather he thinks it's the storm that has stopped his father coming home. I've told him that Dad is not coming home.'

She pauses.

'I thought about what it would be like if he was killed many times, of course, but I never imagined the void, the emptiness. The emptiness is terrible. We had so much ahead of us.'

It is unlikely that anyone will ever know what happened to Lafaille on Makalu. Katia recently flew over the mountain in a helicopter to see if there was any trace of her husband, but it is now very doubtful that his body will ever be recovered. The probability is that he fell into a crevasse shortly after leaving his tent, not long after pulling on his boots, making a final phone call home and stepping out into the cold. There would, of course, be no hope of rescue. Just the silence of the high, high mountains an hour before dawn.