Were patchd both beneath and aboon;

unburnt carbon deposits that had finally ground the big tractor to a halt. A couple of others had rigged up a makeshift distillation unita petrol drum, almost full, with a thin metal tube packed in ice leading from its top to an empty drum. Petrol, Hillcrest had explained, had a lower boiling point than sugar, and when the drum was heated the evaporating gas, which would cool in the ice-packed tube, should emerge as pure petrol. Such, at least, was the theory, although Hillcrest didn't seem absolutely sure of himself. He had asked if we had any suggestion, whether we could help him in any way at all, but I had said we couldn't. I was tragically, unforgivably wrong. I could have helped, for I knew something that no one else did, but, at the moment, I completely forgot it. And because I forgot, nothing could now avert the tragedy that was to come, or save the lives of those who were about to die. My thoughts were black and bitter as the tractor roared and lurched and clattered its way south-west by west under the deepening darkness of a sky that was slowly beginning to fill with cloud. A dark depression filled me, and a cold rage, and there was room in my mind for both. I had a strange fey sense of impending disaster, and though I was doctor enough to know that it was almost certainly a psychologically induced reaction to the cold, exhaustion, sleeplessness and hungerand a physical reaction to the blow on the headnevertheless I could not shake it off: and I was angry because I was helpless. I was helpless to do anything to protect any of the innocent people with me, the people who had entrusted themselves to my care, the sick Mahler and Marie LeGarde, the quiet young German girl, the grave-faced Margaret Rossabove all, I had to admit to myself, Margaret Ross: I was helpless because I knew the murderers might strike at any time, for all I knew they might believe that Hillcrest had already told me all I needed to know ana that I was just waiting my chance to catch them completely off guard; on the other hand they, too, were almost certainly just biding their time, not knowing how much I knew, but just taking a calculated gamble, letting things ride as long as the tractor kept moving, kept heading in the right direction, but prepared to strike once and for all when the time came: and, above all, I was helpless because I still had no definite idea as to who the killers were. For the hundredth time I went over everything I could remember, everything that had happened, everything that had been said, trying to dredge up digital camera memory card guide from the depths of memory one single fact, one isolated word that would point the finger in one unmistakable direction. But I found nothing. Of the ten passengers Jackstraw and I had with us, six of them, I felt certain, were almost beyond suspicion. Margaret Ross and Marie LeGarde were completely beyond it. The only things that could be said against Mrs Dansby-Gregg and Helene was that I hadn't absolute proof of their innocence, but I was certain that such proof was quite unnecessary. United States senators, as recent bribery and corruption cases had lamentably shown, had as many human failingsespecially cupidityas the next man: but, even so, the idea of a senator getting mixed up with murder and criminal activities on this massive scale was too preposterous to bear further examination. As for Mahler, I was quite aware that being a diabetic didn't bar a man from criminal pursuits, and he could have been one of the guilty menjust possibly, he had thought they would force-land near some easily available insulin supplies. But that was just a little too far-fetched, and even if it weren't, I wasn't seriously interested in Mahler. I was concerned with killers who might kill again at any moment, and he most certainly wasn't included in that category: Mahler was a dying man. That left only Zagero, Solly Levin, Corazzini and the Rev. Smallwood, and the Rev. Smallwood was too good notto be true. The Bible was hardly ever out of his hands these days: there were certain lengths to which any impostor might reasonably be expected to go to convince us of his identity, but lengths such as these passed the bounds of the superfluous into the realms of the ridiculous. I had reason to suspect Corazzini. As a tractor specialist, he knew precious little about tractorsalthough I had to be fair and admit that Citroen and Global tractors were a quarter of a century different in time and a world different in design. But he had been the only person I had found on his feet when I had opened the door of the passenger cabin in the plane. It was he who, back in the IGY cabin, had questioned me so closely about Hillcrest's movements. It was he, I had learnt, who had helped Jackstraw and Zagero bring up the petrol from the tunnel and so had the opportunity to spike the stuff left behind. Finally, I believed he could be utterly ruthless. But there was one great point in his favour: that still-bandaged hand, token of his