We settled to our wait. To me it seemed absurdly hopeless. The flying field was on a slight rise. Below us spread the dark shadow that was Constantinople. There was no moon to give it form and substance—it was just a lake of deeper darkness, a spreading mass of silent roof-tops and minarets. How did Brice expect to see his quarry escape? Suppose he fled during the night? And even with daylight—

The first streaks of dawn found us still waiting, our ears strained for the hum of an airplane motor. But hardly had the golden rim of the sun appeared over the horizon when it came. It came from the east—straight out of the golden glory of the sun. Nearer and nearer it came; an airplane—alone.

"It hasn't got the glider," muttered Foulet and his tone was tinged with disappointment. But hardly had he spoken when, from one of the myriad roof-tops below us, rose a swift streak of shadow. So fast it flew, with such unbelievable speed, that to our eyes it was little more than a blur; but—

"The glider!" Brice gasped. "My God! How did he do it?" We stared, silent with amazement. The airplane, that only a second before had flown alone, now was towing a glider—a glider that had arisen, as if by magic, from the housetops!

Another instant and we had piled into the cockpit of the tri-motored plane and were off on our pursuit. That pursuit that led us on and on till, as the sun sank behind us, we found ourselves above the illimitable, tawny wastes of the great Arabian Desert.

And now—what? All day long, as I have said, the plane we were pursuing had maintained, but never increased, the distance between us. Each hour had brought us renewed hope that the next hour would bring capture—or at least some definite clue, some shred of information. But the plane, still towing its glider, had gone on and on, steadily, imperturbably. And we dared not open fire and attempt to bring it down for fear of destroying our one meager chance of following it to its destination.

And now it had vanished. Suddenly, unaccountably it had taken on that terrific burst of speed which I have described. In ten minutes it had become a speck on the far horizon—in another instant it was gone. We were alone. Night was falling. If we turned back our gas might bring us to safety. If we went on—what?

I turned to my companions. Foulet still maintained his non-committal attitude, but Brice was deeply disappointed and worried. His ruddy English face was knotted in a scowl and his blue eyes were dark. Quickly he jerked his head back. We understood. Of course, turning back was the only thing to do; to go on was absurd. Our quarry had totally disappeared. But it was heart-breaking. Once again we had been fooled and outwitted. Our disappointment filled that tiny cockpit like a tangible mist. Brice threw over the stick with a gesture of disgust. In response our right wing lifted a bit, seemed to shake itself, then settled—and the plane continued on its course. Brice's eyes flickered with surprise. He shoved the stick back, threw it over again, but toward the opposite side. Obediently our left wing lifted as if to bank, a shudder passed through it, it dropped, the plane leveled, and went on.

Foulet leaned forward, his eyes were gleaming, his face flushed and eager. "Climb!" he yelled above the roar of the motors. "Up!" Brice nodded—but it was no use. That plane was like a live thing; nothing we could do would swerve it from its course. We stared at one another. Were we mad? Were we under a hypnotic spell? But our minds were clear, and the idea of hypnosis was absurd, for we had tried to turn back. It was the machine that refused to obey.

Again Foulet leaned forward. "Drop!" he shouted. Brice nodded, but the plane refused to respond. On and on, straight as a die, it sped.

"Try slowing the motor," I yelled into Brice's ear and both Foulet and I leaned forward to watch results.

The motors slowed. Gradually the roaring, pounding hum lessened, and our speed continued! The whine of the wind in the wires abated not one whit! The speedometer on our instrument board climbed!

Brice turned. His face, in the deepening dusk, was a blur of pasty white. His hands hung at his sides. The motors purred, pulsed, were silent. The plane, unaided, unguided, flew alone!

We sat hushed and unbelieving in that terrible, deathlike silence. Our ears, attuned all day to the deafening roar of the motors, felt as if they would burst in the sudden, agonizing stillness. There was not a sound save the whine of the wind in the wires as the plane sped on. Above us curved the illimitable arch of darkening sky. Below us lay the empty stretch of blank desert.

We didn't speak. I know that I, for one, could not bring my voice to break that ominous stillness. Silently we sat there, watching, waiting.... The quick darkness of the desert fell like a velvet curtain. The stars burst forth as if lit by an invisible hand. Foulet stirred, leaned forward, gasped. My eyes followed his gaze. Before our plane spread a path of light, dull, ruddily glowing, like the ghost of live embers. It cut the darkness of the night like a flaming finger—and along it we sped as if on an invisible track!

"The speed of that other plane," muttered Brice, breaking that utter silence, "This was it!"

Foulet and I nodded. Well could I imagine that we were travelling at that same terrific, impossible speed. And we were helpless—helpless in the clutch of—what? What power lay behind this band of light that drew us irresistibly toward it?

The ruddy pathway brightened. The light grew stronger. Our speed increased. The whine of the wires was tuned almost past human hearing. The plane trembled like a live thing in the grip of inhuman forces. A great glowing eye suddenly burst from the rim of the horizon—the source of the light! Instinctively I closed my eyes. What power might that eye possess? The same thought must have struck Brice and Foulet for they ducked to the floor of the cockpit, pulling me with them.

"Take care!" Brice muttered, "It might blind us."

We sat huddled in that cockpit for what seemed an eternity, though it couldn't have been more than two minutes. The glare increased. It threw into sharp, uncanny relief every tiny detail of the cockpit and of our faces. The light was as powerful as a searchlight, but not so blinding. It had a rosy, diffused quality that the searchlight lacks.

In that eternity of tense waiting I tried to collect my thoughts. I told myself that I must keep steady, that I must keep my mind clear. I struggled to get a grip on myself; the light, the steady flying without power, the boundless, horrible silence had shaken me. But there was more to come. I knew it. We all knew it. And it was not physical strength that would pull us through—it was wits. We must hold steady. Thank God we all had years of training—war experience, peace experience, countless life-and-death adventures—behind us. It would all count now. It would all help us to keep out brains clear and cool. Wits, I thought again, only our wits would stand between us and—what?

The ground wheels of the plane struck something solid; rolled; stopped! The light snapped off. The sudden blackness, falling like a blanket of thick fur, choked me. In that first dazed, gasping instant I was conscious of only one thing. The plane was no longer in motion. But we had not dropped; of that I was sure. We were still, as we had been, close to two thousand feet above the earth!

Then came the sound of running feet and a confused blur of voices. The door of the cockpit was thrown open. A man leaned in, his hand on the jamb.

"Inspector Brice," he said quietly. "Monsieur Foulet. Lieutenant Ainslee. We are glad to welcome you." His words were courteous, but something in his tone sent a tingling chill down my spine. It was cold, as soulless as the clink of metal. It was