The petrol took a long time to replace, and even with the care we took, it splashed around and had us reeking and light-headed. At last, when the sun was well down in the afternoon sky, Javitz tossed down the coffee-pot he had been using to transfer the liquid, and we were ready.

He spent some time warning the boys about the danger of the fumes and traces that remained on their utensils, and more time explaining to the larger boy, in painful detail, how to work the prop and exactly what the consequences would be if the boy did it wrong.

He climbed back, I dropped my cover down, and we crossed our fingers. When he shouted his command, the lad yanked hard on the propeller. The engine sputtered and died, and Javitz shouted for him to do it again. On the fourth try, the engine cleared its throat and came to life.

When the boys were well clear of the wings, Javitz aimed our nose down the mild slope we had landed on, and opened the throttle.

Hard.

The engine noise built as 230 horses stirred themselves to life. We rattled and rumbled over the field, bouncing and nearly flipping over. My teeth felt loose in my jaw, and each bounce left us only slightly closer to air-bound.

There was a rock wall at the far end of the field, and we were coming at it fast.

Too fast. It looked as high as a building and was certainly solid enough to smash us to pieces. I caught only glimpses past my pilot's shoulders, but I was in no doubt that the rocks were there, greedy for our fragility, vanishing with each bounce, only to reappear closer and higher than before. Three times this happened, and I closed my eyes and drew down my head, because when we descended again, we should be on top of it.

But we did not descend. The wings clawed at air, and the wheels kissed the stones in passing, then before us was only the violet expanse of the heavens.

Exultation lasted perhaps thirty seconds, before it penetrated my mind that the lighter portion of sky was to our right. I rapped on the glass, then unlatched it and wrestled it up a crack to shout, “Mr Javitz, why are we going south?”

There was no response; between the noise and the partition, communication threatened to be a one-way event. I drew breath and shouted more loudly: “We're going south!”

I thought he had still not heard me-either that, or was refusing to acknowledge it. Then I saw that he was bent over something held near his lap. After a minute, he held up a note-pad on which he had printed:

BE NIGHT IN EDINBURGH.

I protested, loudly, cursing that my revolver was in the storage locker, but before I could excavate through my layers of clothing for the knife, I realised he was right: I had to trust his decisions. If we could get safely to Edinburgh, we would be going there.

We made it back to the air field near York well before dark. Fortunately for the laconic individual who had sold us the petrol earlier, Javitz did not find him, and when he laboriously filtered the new petrol through his cloth, not a trace of foreign matter showed up. We spent the night in a nearby farmhouse that let rooms, and before it was truly light, the farmer motored us back to the air field and swung the prop for us. In minutes, the clamour drew us forward and into the sky.

I had, I need hardly mention, given up any real expectation that this northward journey would be anything but a wild-goose chase. I was by now quite certain that Holmes would be closing in on Bergen, and he and Mycroft's men would be baying on the trail of Brothers and his captives.

For me, onward motion was merely a thing to cling to until someone told me to stop.

WE COVERED THE TWO HUNDRED MILES TO Edinburgh in no time at all, the machine demurely slipping northwards as if in all the days since it had rolled out of the shop, it had never so much as hesitated.

This time, the problem lay not in the engine, but outside: As we flew north, the clouds tumbled down to meet us.

Fifty miles south of Edinburgh, the wind began-and not just wind, but rain. One moment we were grumbling along in the nice firm air, and the next the bottom dropped out of the world. It seemed eerily quiet as I rose out of my seat, stomach clenched and my skin shuddering into ice-until the machine slammed into air again and I was suddenly heavy as the propellers bit in and pulled us forward once more. It had happened so quickly, Javitz had not even shifted his hands on the controls. He glanced over his shoulder and laughed, more in relief than amusement. We climbed, I breathed, deliberately, and unclenched my rigid fingers from the seat. Two minutes later it happened again, only this time when the hole ended and we were buoyed and beginning to climb, a sudden gust from the side nearly slapped us over. Javitz fought the controls, raised our nose, and held on.

Then drops began sporadically to spatter my glass cage. Most of it blew past Javitz, but his hand came up several times, wiping his face.

It made for a long fifty miles, tumbling and tossing in the clouds. We came out of the mid-day murk alarmingly close to the ground, and Javitz corrected our course to point us at the aerodrome. A gust hit us just short of the ground and we hit the grass with a terrifying crack from below.

The American gingerly slowed the machine, and I waited for him to turn us about and head back to the hangers we had flashed past. Instead, he throttled down the motor, then stood to look back at the buildings: It seemed that we were to walk back to the aerodrome. I popped up the cover and started to rise, but he stopped me.

“Stay right there. We need your weight.”

“Sorry?”

“If you get out,” he explained impatiently, “we'll shuttlecock. Flip over.”

“I see.” I sat firmly in my seat, thinking heavy thoughts, until I heard voices from outside.

Two large men clung to the wings, the wind bullying us back and forth, while we came about and made our way back to the aerodrome. Only then was I permitted to climb down. I felt like going down on quivering knees to kiss the earth.

One of the men directed me to a café adjoining the air field, where I went in a wobbly scurry while the rain spat down and Javitz tied down the machine and contemplated the wounded undercarriage.

In the shelter of a room with a baking coal stove, I peered through the window and amended my thought: It appeared we would be making arrangements for repairs as well. Javitz and a man in a waterproof were squatting on either side of the right wheel, peering at where the struts connected with the body.

I closed my eyes for a moment, then turned and looked at the waitress. “Would it be possible to have something hot to eat? It looks as though I shall be here for a while.”

She was a maternal sort, and ticked her tongue at my state. “We'll get you something nice and warming,” she said, beginning with drink both hot and stout. I allowed her to slip a hefty and illicit dollop of whisky into the cup of tea before me, and downed the tepid atrocity in one draught. It hit me like a swung punching bag, but when the top of my head had settled back into place, I found that the impulse to pull out my revolver and begin shooting had subsided as well.

I placed the cup gently back into its saucer, took a couple of breaths, and decided that the day was not altogether lost. The men would fix the strut, the wind would die down, we would be in Orkney by nightfall.