Breakfast, such as it was, was waiting and ready to be eaten as soon as the tractor had stopped, but I had little appetite for it: it seemed to me I had forgotten what sleep was like, I had had none for almost three days, I was living now in a permanent state of physical and mental exhaustion and it was becoming almost impossible to concentrate, to think of the hundred and one things that had to be thought of all the time. More than once I caught myself nodding and dozing off over my cup of coffee, and it was only with a conscious effort of will that I forced myself to my feet to keep the radio schedule. I was going to call both Hillcrest and our base – Hillcrest had given me the frequency the previous evening. I decided to call Hillcrest first.

We got through without any difficulty, although Hillcrest said they could hear me only very faintly. I suspected some fault on the generator side, for our receiver was powered by a hundred-hour battery and we could hear Hillcrest's voice clearly.

All the men except Mahler were gathered round me during the transmission – they seemed to find a peculiar reassurance in another voice – however distant and disembodied that voice – and even Zagero and Levin were only seven or eight feet away, sitting in front of the tractor sled with their feet still bound. I was on a canvas chair, with my back to the canvas screen, and Corazzini and Brewster were sitting on the tailboard, the canvas curtains drawn behind them to keep the heat in the cabin. The Rev. Smallwood was behind me, turning the generator handle, and Jackstraw a few feet away, watchful as ever, the cocked rifle ready in his hand.

"Receiving you loud and clear," I said to Hillcrest. My hands were cupped round the microphone and I was holding it close to my mouth to cut out as much as possible of the background noise of the wind. "What progress?" I threw the receiver switch into the antenna, and Hillcrest's voice came again.

"Great!" He sounded enthusiastic, excited. "My congratulations to your learned friend. Works like a charm and we're going like a bomb. We are approaching the Vindeby Nunataks and expect to be through by this afternoon."

This was wonderful news. With any luck he would be up with us late in the evening of that day, and we would have the moral support of his company and the even more important technical resources of everything his big modern Sno-Cat could offer. And Jackstraw and I could get some desperately needed sleep. ... I became aware that Hillcrest was continuing, his voice still charged with the same suppressed excitement.

"The Admiralty or the Government or whoever it is have loosened up at last! Brother, you're sitting on dynamite and you don't know it. You've got it right there with you and you could exchange it tomorrow for a million pounds in the right place. No wonder the Government were so cagy, no wonder they knew something fishy was going on and mounted the biggest search ever. The carrier Triton's going to collect it personally – "

I threw the receiving switch.

"For heaven's sake!" I shouted in exasperation – an exasperation, I was dimly aware, shared by all the others who were leaning forward to hear Hillcrest's voice. "What are you talking about? What was the plane carrying? Over."

"Sorry. It's a guided-missile mechanism of such advanced design and so top-secret that its details, I gather, are known only to a handful of scientists in all the United States. It's the only one of its kind, and was being sent to Britain for study under the recent agreement to share knowledge on atomic weapons and guided missiles." Hillcrest's voice was calm now, measured and sober.

There was a pause, then he went on, slowly, impressively. "I understand the governments concerned are prepared to go any lengths – any lengths – to secure the recovery of this mechanism and prevent its falling into wrong hands."

There was another, longer pause: Hillcrest, clearly, was giving me an opportunity to say something, but I just didn't know what to say. The magnitude of the entire thing took my breath away, temporarily inhibited all thought and speech. . . . Hillcrest's voice was coming through again:

To help you identify this mechanism, Dr Mason. It's camouflaged, made up to look like an ebonite and metal portable radio of fairly large size, with a braided leather carrying strap. Find that portable, Dr Mason, and you'll – "

I never heard the end of that sentence. I was still sitting there, dazedly wondering why the words 'portable radio' should have triggered off such a clangorous bell in my mind -1 can only plead my extreme physical and mental exhaustion – when Zagero catapulted himself off his seat on the sled, knocking Jackstraw staggering, took one tremendous hop with his bound feet just opposite where I was sitting and hurled himself bodily towards Corazzini who, his face twisted in a vicious and unrecognisable mask, had pushed himself off the tractor tailboard with one hand and with the other was fumbling desperately to bring something out from under his coat. He saw he couldn't make it in time, threw himself to one side, but Zagero, bound though he was, was like a cat on his feet and I knew that instant, that instant that was too late, that Zagero was indeed the world-class boxer that he claimed to be. If the astonishing speed of his reflexes were not proof enough, that blurring right arm of his carried with it lethal conviction. Corazzini was a very big man, six feet two and at least two hundred pounds and he was swathed in many layers of heavy clothing, but when that fist caught him with such frightening power just under the heart he staggered back against the tailboard and slid slowly to the ground, unseeing eyes turned up to the first driving flakes of the newly fallen snow. I had never seen a blow delivered with such power: nor do I ever want to see it again.

For perhaps five seconds no one moved, no one spoke, men were held in thrall. The soughing, wailing moan of the wind on the ice-cap sounded weirdly, unnaturally loud. I was the first to break the silence. I was still sitting on my canvas stool.

"Corazzini!" I said. "Corazzini!" My voice was barely more than a whisper, but Zagero heard me.

"Sure it's Corazzini," he said levelly. "It always was." He stooped, thrust his hand under the unconscious man's coat and brought out his gun. "You'd better keep this, Doc. Not only do I not trust our little playmate here with toys like these, but the state prosecutor or district attorney or whatever you call the guy in England will find that the riflin' on this barrel matches the riflin' marks on some very interestin' bullets."

He tossed the gun across, and automatically I caught it. It was a pistol, not an automatic, and it had a strange-looking cylinder screwed on to the front of the barrel. A silencer, I supposed; I had never seen one before. Nor had I ever seen that type of gun before. I didn't like the look of it at all, and I guessed it might be wise to have a gun in my hand when Corazzini came round. Jackstraw, I could see, already had his rifle lined up on the unconscious man. I placed the pistol on the ground beside me and pulled out the Beretta.

"You were ready for him." I was still trying to put things in order in my own mind. "You were waiting for the break. How – "

"Do I have to draw a diagram, Doc?" There was no insolence in his voice, only weariness. "I knew it wasn't me. I knew it wasn't Solly. So it had to be Corazzini."

"Yes, I see. It had to be Corazzini." The words were automatic, meaningless. My thoughts were in a state of utter confusion, as confused, no doubt, as those of Corazzini who was now pushing himself groggily into a sitting position, but for the past fifteen seconds another bell had been ringing far back in my mind, not so loud as the first but even more desperately insistent, and all at once I had it and began to rise to my feet. "But there were two of them, two of them! Corazzini had an accomplice – " That was as far as I got when some metal object smashed across my wrist with brutal force, sending my Beretta flying, and something small and hard ground viciously into the back of my neck.