There's a scrabbling outside the tent and a torch beam flashes against the door. "Hellooo!" offers a small, apologetic voice. William, our waiter and porter, has been waking us every morning for the past week with his hellooo and a cup of tea, but today is different because it's still only 11pm. I've been anticipating this wake-up call with nervous dread not only for the past 3 hours I've lain awake, but for the twenty-or-so years that I've been dreaming about climbing Kilimanjaro. Our campsite is perched high amongst a jumbled mess of rock and scree just below the crestline of the Barafu ridge. At 4600 metres, it's been an achievement just to get here; the altitude has us gasping for breath with the slightest movement. Our tents are the lowest on the site, a heart-thumpingly-breathless 30 metres below Barafu's ridgeline, which boasts the long-drop toilets with the finest views in the world. Bozzy beats me and Etsuko to the mess tent, but there's little enthusiasm for the porridge that William has brought, so we fidget making nervous adjustments to our seven layers of clothing and try to crack jokes. Cobra appears at the tent door, telling us that he and John are ready, so we put on gloves before shaking hands comically and tottering out into the cold and the darkness. Already, a line of lights - the headtorches of German and American climbers from the tents above ours - can be seen making its way along the ridge above us. Cobra leads us up to join them at his characteristically fast pace; we're breathing hard by the time we join the train ten minutes later. The pace immediately slackens and we are aware of German voices coming from the slowly moving shapes ahead, English voices behind. We turn onto the ridge as it rises to meet the mountain, and try to settle into the climb. The first part comes as something of a shock. It's steep and in the darkness we're forced to use hands and walking poles to make progress. At times we queue, stuck behind climbers finding the going tough. Guides can be heard shouting advice and encouragement. Other voices are impatient. As we wait, Cobra turns and hisses, "Drink!" and we do, finding the water in our bottles already desperately cold despite our bottles' thick insulation. As we climb I become aware of a strong feeling of nausea, and fear altitude sickness as I wonder whether I'll throw up, but the nausea passes as we move higher up the ridge. I look up at the stars and suck in air. We pause and John appears, urging us again to drink. Bozzy complains to John that he's finding his breathing difficult, so John rearranges our marching order before we resume: he leads, followed by Etsuko, who has started strongly. I'm in the middle of the group, ahead of Bozzy, with Cobra bringing up the rear. To help Bozzy cope with his breathing, John sets a funereally slow pace and we're soon left behind the other climbers, seeing them only as a succession of twinkling lights zigzagging up the summit cone far above us. I start to relax into the climb, concentrating hard on my breathing, taking for every step a deep lungful of air, inhaled through the nose and out through the mouth. I'm aware of how vital it is to set a rhythm - get breathless at this altitude and it takes an awfully long time to recover. For every thirty-or-so steps I'm taking a sip of water; we've been drinking at least 3 litres - usually 4 or 5 - a day for the past week. Staying hydrated is vital in fending off altitude sickness. We're all nervous of the altitude, knowing that the lack of oxygen could kill us in hours if we're not careful, or get unlucky. Estimates of the death rate amongst Kilimanjaro climbers vary wildly according to which set of figures you believe, but generally range from 1 death for every 10,000 climbers down to 1 in every 3000. Whichever estimate you take, that's frighteningly short odds from where we stand right now. Our slow progress continues. Occasionally I look upwards to the sky, and on three separate occasions I'm lucky enough to see shooting stars. Omens, perhaps? Otherwise my world is all about breathing properly and drinking water, and staring numbly at my feet and the small patches of stone ahead of them that are illuminated by my headlamp. That's all it is: breathing and water and stone.

Etsuko's water bottle freezes first and John calls a halt. He and Cobra tip water from their spare bottles into her throat. She chokes and water runs down her chin, soaking her scarf. She's getting very cold and the wind, which started as a gentle breeze soon after we left camp, has become an icy blast, flinging ash into our faces and robbing her body of warmth. We set off again, John setting a faster pace to help keep us warm, but Bozzy is soon speaking to him about his breathing and John adjusts our pace to a crawl. We've been climbing for several hours now and I'm frustrated at our slow pace. I bash my sticks against the rocks in my frustration. Checking my altimeter doesn't help: three and a half hours of climbing has only seen us ascend 400 metres. We've still got 895 to go. I can't imagine that John and Cobra will let us carry on at this pace for much longer. My dreams of making the summit fade. But John leads us onwards and soon I'm lost in my world of breathing, water and stone.

A couple of hours later and John calls a halt. Is he going to turn us around? He gets out of his pack a flask of hot, sweet ginger tea. Etsuko is shivering, so John and Cobra remove her sodden scarf, wipe her face carefully and fix on her face a woollen mouth guard that gives her the look of Hannibal Lecter. "In one hour the sun will be up and your troubles will be over." says John. Bozzy senses we're nearly at the summit. "Will we be at the top then?" he asks. I see John's rueful smile in my headtorch. "Not unless we move really, really quickly," adds Cobra, with a chuckle. And so it proves. An hour later and I can make out the snout of the Rebmann glacier glowing grey above and to our left. The sky is beginning to lighten. The lowest part of the glacier is about two-thirds of the way up our climb but it takes another half-hour to reach it. By now, all our water bottles have frozen and the wind is whipping straight into our faces on the rightward leg of each zigzag. Our pace is still horribly slow and it's clear that if we are to reach Stella Point, on the rim of the crater, it won't happen until well after sunrise. Presently, Cobra taps me on the shoulder and points off to the right. I see the jagged outline of Mawenzi, Kilimanjaro's second peak, and realise it's below us. Over Mawenzi's shoulder is a chink of sunlight that slowly grows until it suddenly blasts across the sky, illuminating the frosty plains of the Saddle - the high altitude plain between Mawenzi and the main peak, Kibo - far below us. I get my video camera ready to record the moment, but realise with a lurch in my stomach that the battery is almost flat and the tape is at an end: in my oxygen deprived state I must have turned it to record at Barafu and then put it back in its bag, still recording. I try to warm the battery in my hands, rewind the tape a little and point the camera towards Mawenzi and the sunrise, with more hope than conviction. John watches us with interest, then removes our headtorches and urges us to continue upwards. We do, and before long we are meeting climbers coming down and past us, successful summiteers whose stares I avoid, afraid of seeing smugness, or pity. One climber is in a bad way with altitude sickness; she's lurching drunkenly and looks exhausted as a guide leads her by the arm. I turn away and try to concentrate on the breathing and the stones. As more climbers pass by I wonder if we still have a chance to make it, or will our guides turn us back. But John keeps leading us upwards, ever so slowly. The sun is higher in the sky and only the odd climber or two is still coming down past us. Most, however, have already left the mountain. The scree is steep and I can see, maybe 200 metres above, a couple more climbers begin their descent from Stella Point. The Point - just a gap in the crater rim - has been in view for a couple of hours now and doesn't appear to have got any nearer. We'll never make it, I think. I start to watch my feet, and begin laughing at how slowly they move. First one will advance a couple of inches, then the other will join it. Then that one will forge ahead half a bootlength, before the other catches it up. I laugh out loud. My mind goes back to the training runs I did along the old railway trackbed by the river Taw. Did all that training help me? It doesn't matter now; we're too late. My mind tells me that I'm running now, along the old trackbed, gasping for breath and parched by the hot sun. I can hear a train coming, the engine panting hard, its exhaust beat roaring louder as it comes closer, ringing through my ears and filling my head. It's going to crush me and I don't care. Suddenly, I'm back in the present, and Cobra is forcing ice-cold water into my mouth. I choke and spit, and the roaring of my breath comes harder as I gasp for air. He looks into my face and I signal that I'm okay. I hope I've fooled him. We continue upwards, no longer on a path but on a moving conveyer belt of scree that makes a mockery of our attempts to climb it.

After an hour I look up and realise with surprise that I'm only ten or so vertical metres from Stella Point. Etsuko is slightly ahead of me, Bozzy behind. I lunge for the last few yards, my breathing reaching a wild crescendo, when suddenly a flash of white light and a sharp pain in the chest wind me. I stagger forward onto my poles, gasping furiously for air. I'm not sure what's happened. Cobra is beside me, asking if I'm okay, but I feebly wave him away with my fingers. It feels like my strength has all drained and I take a few more seconds to rest. When I continue, I do so even more slowly, aware of a weakness about my knees and a lightness in my head. I take shallower breaths and try to regain my rhythm. I think of Simon and wonder if he's watching and whether he can help, and keep going as the gradient begins to ease off. Looking up, I see not stones but glacial ice and the inner crater of the mountain. We've reached Stella Point - Bozzy and Etsuko are there ahead of me, smiling and gasping in air, so I slump beside them on the rock, thoroughly exhausted. We pause a few moments and look along the crater rim to our left. High above us, at the far end of the ridge, I can just make out the famous signpost at the summit of Uhuru Peak. "It's 40 minutes from here." says John and as we set off, Cobra starts to sing a song, "You're going to win the war, You're going to beat the mountain." He's been singing it all week, and I'm still not sure whether to believe him. Sensing victory, Bozzy sets off at a fast pace, but the initial climb away from Stella Point is quite steep and we soon overhaul and pass him. The path winds upwards, steeper than I'd expected, and our progress remains slow. Although it's still cold and our water remains frozen, the sun is high in the sky and glints off the walls of the glacier to our left. Underfoot, the scree has been replaced by compacted rich brown earth and the walking is easier. "We're nearly there!" shouts John from behind, and I make an effort to catch up with Etsuko so that I can share the moment with her. But something is wrong. As I get near, she stops, slumps forward onto her walking poles, then buckles at the knees and begins to slide to the ground. Immediately, Cobra is beside her, catching her fall. Her eyes are closed. "I'm so tired." she says. John is by her side now and tells her how close we are. "You'll make it, but you must keep going." he implores. Cobra grabs her arm and pulls her forward. She lurches drunkenly and her head lolls back, but her feet start moving, and keep moving, more sideways than upward, but upward nonetheless. John takes her other arm and they look like friends helping a drunk into a taxi. Somehow, Etsuko keeps her legs moving and, stumbling, she climbs the final rise. A moment later Bozzy and I have climbed it too, seeing the summit sign together. It's just a few metres away and Etsuko, John and Cobra sway towards it as my eyes start to moisten. The summit - all ours - is at once fearsome and deathly, yet incredibly beautiful, the air clear, the colours bright. There are hugs, tears and photographs. Cobra waves the video camera around as Etsuko and I slump below the summit sign. He asks me how it works but I've given up on it. He pretends it's working anyhow. Strange things happen up there where the brain is short of oxygen: one of our porters - unbelievably - approaches along the summit ridge. It's Emmanuel, who's had the dubious honour of carrying my overweight trekking bag all week. He's wearing no special gear and no rucksack with supplies. He's just come to check that we're all okay. He speaks to John for a moment, then heads off down the mountain.

We don't stay long - lingering could be deadly. We make our way down past Stella Point in quick time, Etsuko seemingly recovered from her exhaustion. But the ridge between Stella and Gillman's Point, where we'll start to descend the summit cone, is rocky and has some short inclines. Etsuko makes two steps up the first of these, then collapses once more. It's obvious that she's far from well, and needs to descend quickly. Cobra and John take turns guiding her to Gillman's, but it's laborious progress and she needs to halt often. At Gillman's, John hands out energy drinks and crisps, and we start to descend from the crater rim. Yet after just 4 or 5 metres our progress is brought to a halt as Etsuko collapses onto the ground. She can't make it down some of the rock steps. Sitting against a rock, her head is lolling from side to side. She complains that her waterproof over-trousers are too tight, so we remove them for her, struggling to get them over her boots. She seems quite incapable of helping herself. I realise how easy it would be to die here, and I wonder if the guides will leave her. Tears start to prick my eyes. But Cobra has other ideas, and grabs her arm, bringing her to her feet. He pulls her down over rock steps, expertly guiding each foot into the best place. Once, she falls backwards, landing painfully, but Cobra picks her up, dusts her down and continues. The rock steps abate and the pair reach a huge scree chute, down which progress is easier. I try to keep up with Cobra's pace, but tired, fail and soon fall behind.

Hours later, whilst I'm still high on the mountain, I can see Cobra and Etsuko far below as they near the Kibo huts at the foot of the summit cone. They are walking together, but Cobra no longer holds her arm: Etsuko is walking unaided. Knowing that she'll be okay, I fall to my knees and choke in deep breaths of air. I care to remember little else of the descent. By the time Bozzy and I reach Kibo huts, Etsuko is well recovered, yet looking very tired, sitting alone at a table by some Americans preparing for their own summit bid. Later, she vomits, and feels better for it, although I suspect the Americans don't. We continue our descent across the dusty saddle, past Mawenzi, and down a bouldery path in the dark to our tents at Horombo. There, William greets us with a "Hellooo" and a huge curry, both of which we ignore, exhaustion being a stronger force than good manners or good food.

Last night I played back the tape from the video camera, more in hope than expectation. Most of the tape shows just a black screen, with muffled, disembodied voices calling from the darkness. But then in the last two minutes, there we are: Etsuko and I sitting in the bright sunshine on the summit. And there too is Cobra's rich, deep voice, raised above the wind, filled with emotion and solemnity, "This is how they made it. This is how they made it. Congratulation! It's alright! Karibu tena! Kilimanjaro! Highest point in Africa!" We wave dementedly at him, and prayer flags billow in the background.