She didn't speak at once. Nobody spoke. Everyone was too stunned, too busy fighting incredulity and trying to assimilate the meaning of the shocking news I'd given them – everyone, that is, except two. But though I scanned eight faces with an intensity with which I had never before examined people I saw nothing -not the slightest off-beat gesture, the tiniest guilty reaction. As for what I'd secretly hoped for – a guilty interchange of glances -well, the idea now seemed hopelessly, laughably improbable. Whoever the killers were, they were in perfect control of themselves. I felt despair touch me, a sure knowledge of defeat.

"I must believe you." Marie LeGarde spoke as slowly as before, but her voice was unsteady and her face drained of colour. She looked at Margaret Ross. "You knew of this, my dear?"

"Half an hour ago, Miss LeGarde. Dr Mason thought I had done it."

"Good God! How – how utterly ghastly! How horrible! Two of us murderers." From her position by the stove, Marie LeGarde glanced round the eight seated people, then looked quickly away. "Suppose – suppose you tell us everything, Dr Mason."

I told them everything. On the way back from the plane with Miss Ross I had debated this with myself – the question of secrecy or not. The no secrecy decision had won hands down: keeping quiet wouldn't fool the killers – they knew I knew: no secrecy would mean each and every one of the passengers inn watching the others like hawks, making my task of constant vigilance all that much easier, the killers' chance of making mischief all that more difficult.

"You will stand up one at a time," I said when I'd finished. "Mr London will search you for your guns. And please don't forget -1 know I'm dealing with desperate men. I'm prepared to act accordingly. When your turn comes stand very still indeed and make no suspicious move, not the slightest. I'm not very good with a pistol, and I shall have to aim at the middle of your bodies to make certain."

"I believe you would at that," Corazzini said thoughtfully.

"It doesn't matter what you believe," I said coldly. "Just don't be the one to find out."

Joss started on Zagero. He searched him thoroughly -1 could see the anger on Zagero's face, but his eyes didn't leave my gun -and found nothing. He moved on to Solly Levin.

"Might I ask why I'm being excused?" Marie LeGarde asked suddenly.

"You?" I said shortly. My eyes didn't move from Solly. "Marie LeGarde? Don't be so damned silly!"

"The choice of words and tone of voice leave a lot to be desired." Her voice was soft and warm, though still shaky. "But I've never had a greater compliment. All the same, I insist on being searched: I don't want to be the one under a cloud if the guns don't turn up."

And the guns didn't turn up. Joss finished searching the men, Margaret Ross the women – Mrs Dansby-Gregg under icy protest – and neither found anything. Joss looked at me, his face empty of all expression.

"Get their luggage," I said harshly. "The small cases they're taking with them. We'll try these."

"You're wasting your time, Dr Mason," Nick Corazzini said quietly. To any characters smart enough to guess that you were going to frisk them, the next move would stick out a mile. A child could guess it. You might find those guns you talk about hidden on the tractor or the sledges or buried under a couple of inches of snow, ready to be picked up whenever required, but you won't find them in our grips. A thousand to one, in dollars, that you don't."

"Maybe you're right," I said slowly. "On the other hand, if I were one of the killers and did have a gun in my case – well, that's exactly the way I'd talk too."

"As you said to Miss LeGarde just now, don't be so damned silly!" He jumped to his feet, walked over to a corner of the cabin under the watchful eyes of Jackstraw and myself, picked up a handful of small cases and dumped them on the floor before me, his own nearest me. "Where are you going to start? There's mine, that's the Reverend's robe case, this" – he picked it up and looked at the initials – 'this is the Senator's brief-case. I don't know whose the last is."

"Mine," Mrs Dansby-Gregg said coldly.

Corazzini grinned. "Ah, the Balenciaga. Well, Doc, who – " He broke off, straightened slowly, and gazed up through the skylight. "What – what the devil is happening up there?"

"Don't try to pull any fast stuff, Corazzini," I said quickly. "Jackstraw's gun – "

"The hell with Jackstraw's gun!" he snapped impatiently. "Have a look for yourself."

I motioned him out of the way and had a look. Two seconds later I had thrust my automatic into Joss's hand and was on my way up top.

The airliner was a blazing torch in the darkness of the night. Even at that distance of half a mile and against the light wind, I could clearly hear the fierce roaring and crackling of the flames -not flames, rather, but one great solid column of fire that seemed to spring from the wings and centre of the fuselage and reach up clear and smokeless and sparkless two hundred feet into the night sky, brushing its blood-red stain across the snow for hundreds of yards around, transforming the rest of the still ice-sheathed fuselage into a vast effulgent diamond, a million constantly shifting points of refracted white and red and blue and green that glittered and gleamed with an eye-dazzling scintillating brilliance that no jewels on earth could have matched. It was a fantastically beautiful spectacle, but I'd had time to watch it for barely ten seconds when the dazzling coloured irradiation turned into a blaze of white, the central flame leapt up to twice, almost three times its original height and, two or three seconds later, the roar of the exploding petrol tanks came at me across the frozen stillness of the ice-cap.

Almost at once the flames seemed to collapse in upon themselves and the perimeter of the blood-red circle of snow shrank almost to vanishing point, but I waited to see no more. I dropped down into the cabin, pulling the hatch shut behind me, and looked at Jackstraw.

"Any chance at all of accounting for the presence of our various friends here during the past half-hour?"

"I'm afraid not, Dr Mason. Everyone was on the move all the time, finishing off the tractor body or bringing up the stores and petrol drums and lashing them on the sledge." He glanced up through the skylight. "The plane, wasn't it?"

" 'Was' is right." I glanced at the stewardess. "My apologies, Miss Ross. You did hear somebody out there."

"You mean – you mean it wasn't an accident?" Zagero asked.

There's a fair chance that you know damned well that it wasn't, I thought. Aloud, I said: "It was no accident."

"So there goes your evidence, eh?" Corazzini asked. "The pilot and Colonel Harrison, I mean."

"No. The nose and tail of the plane are still intact. I don't know what the reason could be – but I'm sure there's a damned good one. And you can put these bags away, Mr Corazzini. We're not, as you say, playing with children or amateurs."

There was silence while Corazzini returned the bags, then Joss looked at me quizzically.

"Well, that explains one thing at least."

"The messed-up explosives?" I remembered with chagrin how I had listened to the abnormally loud hissing out by the plane, but had ignored it. Someone who had known very clearly what he was doing had led a fuse into petrol lines or tanks or carburettors. "It certainly does."

"What's all this about explosives and fuses?" Senator Brewster demanded. It was the first word he had spoken since Jackstraw had scared the wits out of him, and even yet the colour wasn't all back in his face.

"Somebody stole the fuses to set fire to the plane. For all I know it may have been you." I held up my hand to still his outraged spluttering and went on wearily: "It may equally well have been one of the other seven of you. I don't know. All I know is that the person or persons responsible for the murders were responsible for the theft of the fuses. And for the smashing of the radio valves. And for the theft of the condensers."