Both of us were pressed hard in against the ice, motionless, hardly daring to breathe, when I heard a sudden cry of pain from above. It came from Helene – she must have caught her injured shoulder as she was being pulled over the edge of the crevasse. But what caught my eye was not Helene, but Corazzini. He was standing very close to the edge, and he had my gun in his hand.

I have never known such chagrin, such profound despair, such bitterness of spirit – or, to be utterly frank, such depths of fear. The one thing I had guarded against all the time, the one thing I had dreaded above all other things, that Jackstraw and I should ever find ourselves, at the same time, completely at the mercy of the killers, had come to pass. But even in my fear there was savagery – savagery towards the man who had engineered this so beautifully, savagery towards myself for having been so easily and utterly fooled.

Even a child could see how it had been done. The series of snow-bridges had given Corazzini the idea. A little nudge to Helene Fleming at the right place – it was as plain as a pikestaff that it had been no accident – and it was a foregone conclusion that either Jackstraw or myself would have to go down to fix a rope round the youngster who, with her broken collar-bone, would be unable to do it herself: I suppose the possibility that she might have crashed straight through the snow-bridge must have occurred to Corazzini, but a man with a record of killings like he had wouldn't be worried unduly on that score – annoyance at the failure of his plan would probably have been his only reaction. And when one of us had gone down and the other was supervising the rescue from above – well, another little nudge would have solved all Corazzini's problems. As it was, I had played into his hands more completely than he could ever have hoped.

Mouth dry, sweat breaking out in the palms of my clenched fists and my heart going like a trip-hammer in my chest, I was wondering desperately how he was going to administer the coup de grace when I saw the Rev. Smallwood approaching him arms outstretched and saying something I couldn't catch. It was a brave gesture of the little minister's, but a forlorn and hopeless one: I could see Corazzini change his gun to his left hand, strike Mr Smallwood a heavy backhanded blow across the face and the sound of a body falling on the ice above was unmistakable. And then Corazzini was waving the others back at the point of the gun and was advancing towards the wooden battens that straddled the crevasse, and I knew with a dull certainty how he intended to dispose of us. Why waste two bullets when all he had to do was to kick the edges of these battens over the side? Whether these . battens, weighing two hundred pounds between them, struck us or smashed away the last remaining buttress of the snow-bridge was quite immaterial: the point was that I was inescapably attached to them by the nylon rope round my waist, and when they plummeted down I would go with them, tearing away the bridge and carrying Jackstraw with me to our deaths in the unthinkable depths below.

Despairingly, I considered the idea of snatching at the rifle still strapped to Jackstraw's back, but dismissed it even with the thought. It would take me seconds to get it off. There was only one thing for it, and it wasn't going to do me any good at all. With a jump I could be half-way up the rope in a second, the increased weight would make the battens difficult to kick over, and while Corazzini was either pushing these or pumping bullets into me as I swarmed up the rope, somebody – Zagero, say, could get him from the rear. That way there might, at least, be a faint chance for Jackstraw. I swung my arms behind me, bent my knees then remained frozen in that ridiculous position as a rope came uncoiling down from above and struck me across the shoulder. I glanced up and saw Corazzini smiling down at me.

"You two characters fixin' on stayin' down there all day? Come on up."

It would be useless to try to describe the maelstrom of thoughts and emotions that whirled through my mind in the ninety seconds that elapsed before Jackstraw and I stood once more in incredulous safety on the trail above. They ranged from hope to bafflement to wild relief to the conviction that Corazzini was playing a cat-and-mouse game with us, and no one thought was in my mind for more than seconds at a time. Even when I was safe, I still didn't know what to think, the overwhelming relief and gladness and reaction blotted out everything. I was trembling violently, and although Corazzini must have noticed it he affected not to. He stepped forward and handed me the Beretta, butt first.

"You're a mite careless about where you stow your armoury, Doc. I've known for a long time where you kept this. But I guess it may have been fairly useful these last few minutes."

"But – but why-?"

"Because I've got a damned good job and a chair behind a vice-president's desk waiting for me in Glasgow," he snapped. "I'd appreciate the chance to sit in that chair some day." Without another word, he turned away.

I knew what he meant, all right. I knew we owed him our lives. Corazzini was as convinced as I that someone had engineered the whole thing. It didn't require any thought at all to guess who that someone was.

My first thought was for Jackstraw. Jackstraw with a broken arm was going to make things very difficult for me: it might well make things quite impossible. But when I'd worked his parka off it required only one glance at the unnatural twist of the left arm to see that though Jackstraw had had every excuse for thinking his arm gone, it was, in fact, an elbow dislocation. He made no murmur and his face remained quite expressionless as I manipulated the bone back into the socket, but the wide white grin that cracked his face immediately afterwards was proof enough of his feelings.

I walked over to where Helene Fleming sat on the sledge, still shaking from the shock, Mrs Dansby-Gregg and Margaret Ross doing their best to soothe her. The uncharitable thought struck me that it was probably the first time that Mrs Dansby-Gregg had ever tried to soothe anyone, but I was almost ashamed of the thought as soon as it had occurred to me.

"That was a close call, young lady," I said to Helene. "But all's well.. . . Any more bones broken, eh?" I tried to speak jocularly, but it didn't sound very convincing.

"No, Dr Mason." She gave a long shuddering sigh. "I don't know how to thank you and Mr Nielsen – "

"Don't try," I advised. "Who pushed you?"

"What?" She stared at me.

"You heard, Helene. Who did it?"

"Yes, I -1 was pushed," she murmured reluctantly. "But it was an accident, I know it was."

"Who?" I persisted.

"It was me," Solly Levin put in. He was twisting his hands nervously. "Like the lady said, Doc, it was an accident. I guess I kinda stumbled. Someone tapped my heels and – "

"Who tapped your heels?"

"For cryin' out loud!" I'd made no attempt to hide the cold disbelief in my voice. "What would I want to do a thing like that for?"

"Suppose you tell me," I said, and turned away, leaving him to stare after me. Zagero stepped in my way, but I brushed roughly past him and went up towards the tractor. On the sled behind I saw the Rev. Smallwood sitting nursing a bleeding mouth. Corazzini was apologising to him.

"I'm sorry, Reverend, I'm really and truly sorry. I didn't for a moment think you were one of them, but I couldn't afford to take any chances back there. I hope you understand, Mr Smallwood."

Mr Smallwood did, and was suitably Christian and forgiving. But I didn't wait to hear the end of it. I wanted to get through the Vindeby Nunataks, and get through with as little loss of time as possible, preferably before it became dark. There was something that I knew now that I had to do, and as soon as possible: but I didn't want to do it while we were all teetering on the edge of that damned crevasse.