"Solly Levin."

The brief twilight of noon came and went, the cold steadily deepened and by late in the evening it seemed that we had been on board that lurching, roaring tractor all our lives.

Twice only we stopped in the course of that interminable day, for refuelling at 4 p.m. and 8 p.m. I chose these times because I had arranged with Joss that I would try to contact him every fourth hour. But though we set up the apparatus outside while Jackstraw was refuelling and Corazzini sat astride the bicycle seat and cranked the generator handle while I tapped out our call sign for almost ten unbroken minutes, no shadow of an answer came through. I had expected none. Even if by some miracle Joss had managed to fix the set, the ionosphere turbulence that had caused the aurora would have almost certainly killed any chance of making contact. But I'd promised Joss, and I had to keep faith.

By the time I made the second try, everyone, even Jackstraw and myself, was shaking and shivering in the bitter cold.

Normally, we wouldn't have felt it much – in very cold weather we wore two complete sets of furs, the inner one with the fur inside, the outer with the fur outside. But we'd given our extra pairs away to Corazzini and Zagero – furs were essential in that ice-box of a tractor cabin – and suffered just as much as the others.

Occasionally, someone would jump down from the tractor and run alongside to try to get warm, but so exhausted were most from sleeplessness, hunger, cold and eternally bracing themselves against the lurching of the tractor, that they were staggering from exhaustion within minutes and had to come aboard again. And when they did come aboard, the sweat from their exertions in such heavy clothes turned ice-cold on their bodies, putting them in worse case than ever, until finally I had to stop it.

It grieved me to do what had to be done, what I saw must be done, but there was no help for it. The weariness, the cold and the sleeplessness could be borne no longer. When I finally gave the order to stop it was ten minutes after midnight, and we had been driving continuously, except for brief fuel and radio halts, for twenty-seven hours.

Despite our exhaustion, despite our almost overwhelming need for sleep, I don't think anyone slept that night, even for a moment, for to have slept would have been to freeze to death.

I had never known such cold. Even with twelve of us jam-packed inside a tiny wooden box built to hold five sleeping people at the most, even with the oil fire roaring up the chimney all night long and wanned by a couple of cups of piping hot coffee apiece, we all of us suffered agonies during these dark hours. The chattering of teeth, the St Vitus' dance of tremor-ridden limbs knocking against the thin uninsulated wooden walls, the constant rubbing as someone sought to restore life to a frozen face or arm or foot. These were the sounds that never ceased. How the elderly Marie LeGarde or the sick Mahler survived that night was indeed a matter for wonder.

But survive they did, for when I looked at my luminous watch, saw that it was almost four o'clock and decided that enough was enough, both of them were wide awake when I switched on the little overhead light. Weak enough normally, that light was now no more than a feeble yellow glow– an ominous sign, it meant that even the tractor batteries were beginning to freeze up – but enough to see the crowded circle of faces, white and blue and yellowing with frostbite, the smoke-like exhalations that clouded in the air before them with every breath they took, the film of slick ice that already covered the walls and all of the roof except for a few inches round the stove pipe exit. As a spectacle of suffering, of sheer unrelieved misery, I don't think I have ever seen its equal.

"Insomnia, eh, Doc?" It was Corazzini speaking, his teeth chattering between the words. "Or just forgotten to plug in your electric blanket?"

"Just an early riser, Mr Corazzini." I glanced round the haggard and pain-filled faces. "Anybody here slept at all?"

I was answered by mute headshakes from everybody.

"Anybody likely to sleep?"

Again the headshakes.

"That settles it." I struggled to my feet. "It's only 4 a.m., but if we're going to freeze to death we might as well freeze on the move. Not only that, but another few hours in this temperature, and that tractor engine will never start again. What do you think, Jackstraw?"

"I'll get the blow-torches," he said by way of answer, and pushed his way out through the canvas screen. Almost at once I heard him begin to cough violently in the deadly cold of the air outside, and, in the intervals between the coughing, we could clearly hear the dry rustling crackling of his breath as the moisture condensed, froze and drifted away in the all but imperceptible breeze.

Corazzini and I followed, choking and gasping in turn as that glacial cold seared through throat and lungs, adjusting masks and goggles until not a millimetre of flesh was left exposed. Abreast the driving cabin I drew out my torch and glanced at the alcohol thermometer – ordinary mercury froze solid at – 38° – then looked again in disbelief. The red spirit inside the glass had sunk down to within an inch of the bulb and stood on the line of -68° – exactly one hundred degrees of frost. Still well below Wegener's -85°, further short still of the incredible -125° that the Russians had recorded at the Vostok in Antarctica, but nevertheless the lowest, by almost fifteen degrees, that I had ever experienced. And that it should happen now – now, two hundred miles from the nearest human habitation, with Jackstraw and myself stuck with two murderers, a possibly dying man, seven other passengers rapidly weakening from exposure, exhaustion and lack of food, and a superannuated tractor that was due to pack up at any moment at all.

Over an hour later I had cause to revise the last part of that estimate – it seemed that the tractor had already packed up. I had had my first intimation of trouble to come when I had switched on the ignition and pressed the horn – the faint mournful beep could hardly have been heard twenty yards away. The batteries were so gummed up by the cold that they couldn't even have turned over a hot engine, far less one in which the crankcase, transmission and differential were all but locked solid in lubricating oil that had lost all power to lubricate anything and had been turned into a super viscous liquid with the consistency and intractability of some heavy animal glue. Even with two of us bringing all our weight to bear on the starting handle it was impossible to turn even one cylinder over the top.

We made to light the paraffin blow-torches but they, too, were frozen solid: paraffin freezes at just over -50°, and even at -40° it still flows like heavy gear-case oil. We had to thaw them out with a petrol blow-torch, then place all five of them on wooden boxes and behind canvas aprons to retain the heat, two to thaw out the crankcase, two for the gear-box and transmission and the last for the differential. After an hour or so, when the engine had begun to turn fairly easily and we had brought out the heavy battery which had been thawing out by the stove, we tried again. But it gave no sign of life at all.

None of us, not even Corazzini whose Global tractors were all diesel-powered, was an expert in engine maintenance, and this was when we came very close to despair. But despair was the one emotion we couldn't afford, and we knew it. We kept the blow-torches burning, returned the battery to the stove, removed and cleaned the plugs, eased the frozen brushes in the generator, stripped and removed the petrol lines, thawed them and sucked out the frozen condensation by mouth, scraped away the ice from the carburettor intake and returned everything in place. We had to remove our gloves for most of this delicate work, the flesh stuck to metal and pulled off like the skin of an orange when we removed our hands, even the backs of our fingers became burnt and blistered from casual knocks on metal, blood oozed out from under our fingernails only to coagulate in the freezing air, and our lips, where they had touched the copper petrol feeds, were swollen and puffed and blistered. It was brutal, killing work, and in addition to the work our arms and legs and faces were almost constantly frozen, despite frequent visits to the stove to thaw ourselves out. It was murderous – but it was worth it. At six-fifteen, two and a quarter hours after we had begun, the big engine coughed and spluttered into life, missed, coughed again, caught and settled down into a steady even roar. I felt my split lips cracking into a painful grin under my mask, thumped Jackstraw and Corazzini – for the moment quite forgetting that the latter might be one of the killers – on the back, turned and went in for breakfast.