Above us curved the pale, hot bowl of cloudless sky; below us stretched the rolling, tawny wastes of the great Arabian Desert; and away to the east, close to the dipping horizon, scudded the tiny speck we were following. We had been following it since dawn and it was now close to sunset. Where was it leading us? Should we go on or turn back? How much longer would our gas and oil hold out? And just where were we? I turned and saw my questions reflected in the eyes of my companions, Paul Foulet of the French Sureté and Douglas Brice of Scotland Yard.

“Too fast!” shouted Brice above the roar of our motors. I nodded. His gesture explained his meaning. The plane ahead had suddenly taken on a terrific, unbelievable speed. All day it had traveled normally, maintaining, but not increasing, the distance between us. But in the last fifteen minutes it had leaped into space. Fifteen minutes before it had been two miles in the lead; now it was barely visible. A tiny, vanishing speck. What could account for this burst of superhuman speed? Who was in that plane? What was in that plane?

I glanced at Foulet. He shrugged non-committally, waving a courteous hand toward Brice. I understood; I agreed with him. This was Brice’s party, and the decision was up to him. Foulet and I just happened to be along; it was partly design and partly coincidence.

Two days before I had been in Constantinople. I was disheartened and utterly disgusted. All the way from the home office of the United States Secret Service in Washington I had trailed my man, only to lose him. On steamships, by railway, airplane and motor we had traveled--always with my quarry just one tantalizing jump ahead of me--and in Constantinople I had lost him. And it was a ruse a child should have seen through. I could have beaten my head against a wall.

And then, suddenly, I had run into Foulet. Not ten days before I had talked to him in his office in Paris. I had told him a little of my errand, for I was working on the hunch that this man I was after concerned not only the United States, but France and the Continent as well. And what Foulet told me served only to strengthen my conviction. So, meeting him in Constantinople was a thin ray of light in my disgusted darkness. At least I could explode to a kindred spirit.

“Lost your man!” was his greeting. And it wasn’t a question; it was a statement.

“How did you know?” I growled. My humiliation was too fresh to stand kidding.

“Constantinople,” said Foulet amiably. “You always lose them in Constantinople. I’ve lost three here.”

“Three?” I said, “Like mine!”

“Exactly,” he nodded. Then he lowered his voice. “Come to my hotel. We can talk there.”

“Now,” he continued fifteen minutes later as we settled ourselves in his room, “you were very circumspect in Paris. You told me little--just a hint here and there. But it was enough. You--the United States--have joined our ranks--”

“You mean--”

“I mean that for a year we, the various secret service organizations of the Continent--and that includes, of course, Scotland Yard--have been after--Well, to be frank, we don’t know what we’re after. But we do know this. There is a power--there is someone, somewhere, who is trying to conquer the world.”

[Illustration: A white speck took shape beneath the rising Island.]

“Are you serious?” I glanced at him but the tight lines of his set mouth convinced me. “I beg your pardon,” I murmured. “Go ahead.”

“I don’t blame you for thinking it was a jest,” he said imperturbably, “But, to prove I know what I’m talking about, let me tell you what this man has done whom you have been pursuing. He has done one of two things. Either he has proved himself a dangerous revolutionary or he has engineered the failure of a bank or chain of banks--”

“We can’t prove it,” I interrupted.

“No,” said Foulet, “Neither can we. Neither can Scotland Yard--or the secret services of Belgium or Germany or Italy or Spain. But there you are--”

“You mean that in all these countries--?”

“I mean that for a year--probably longer--these countries have been and are being steadily, and systematically, undermined. The morale of the people is being weakened; their faith in their government is being betrayed--and someone is behind it. Someone who can think faster and plan more carefully than we--someone whose agents we always lose in Constantinople! I’ll wager you lost your man from a roof-top.”

I nodded, my disgust at my own stupidity returning in full force. “There was a lower roof and a maze of crisscross alleys,” I muttered. “He got away.”

“Was there an airplane anywhere around?” asked Foulet.

I glanced at him in surprise. What good would an airplane have been on a roof-top ten feet wide by twelve feet long? Then I remembered. “There was an airplane,” I said, “but it was a long way off, and I could scarcely see it; but the air was very still and I heard the motor.”

Foulet nodded, “And if you had had a pair of glasses,” he said gently, “You would have seen that the airplane had a glider attached to it. There is always an airplane--and a glider--when we lose our men from the roofs of Constantinople.”

“But that must be coincidence!” I insisted. “Why, I was on that roof right on the fellow’s heels--and the airplane was at least five miles away!”

Foulet shrugged, “Coincidence--possibly,” he said, “but it is our only clue.”

“Of course,” I murmured thoughtfully, “you have never been able to follow--”

Foulet smiled, “Can you imagine where that airplane would be by the time we climbed down off our roofs and got to a flying field and started in pursuit?”

We descended for dinner. Foulet’s story had restored my self-confidence somewhat--but I was still sore. Of course Foulet connecting my vanishing man with that disappearing airplane was absurd--but where had the man gone? Was my supposition that he had jumped to a lower roof, climbed a wall and run through the maze of alleyways in half a minute in any way less absurd?

We were halfway through dinner when Brice appeared. Brice was one of the best men in Scotland Yard and I had known him many years. So, evidently, had Foulet, for his eyes flickered faintly with pleased surprise at the sight of him. Brice came directly to our table. He was bursting with victorious joy. I could feel it somehow, although his face, carefully schooled to betray no emotion, was placid and casual.

All through the remainder of the meal I could feel the vibrations of his excitement. But it was only at the very end that he confided anything--and his confidence only served to make the excitement and sense of impending thrill greater.

Just as he was rising to leave he shoved a tiny strip of paper across the table to me with a sidelong glance at Foulet. “Another roof-top,” I read scrawled in pencil. “If you like, meet me at the flying field before dawn.” If I liked! I shoved the paper across to Foulet who read it and carelessly twisted it into a spill to light his cigar. But his hand shook ever so slightly.

Needless to say we went to the flying field shortly after midnight. Bruce was there, pacing up and down restlessly. Near him was a huge tri-motored biplane, its motor humming in readiness.

“I’ve put a man on the trail in my place,” Brice told us briefly. “Somebody else is going to lose the scent on a roof-top--and I’m going to watch.”

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 dull, without life or inflection. But there was something else--something I could not name.

I was nearest the door and scrambled out first. To my surprise it was not dark. We were enveloped by a radiance, rosy as the broad ray had been, but fainter, like the afterglow of a sunset. By this light I could make out, vaguely, our surroundings. We seemed to be on a plateau; a great flat space probably an acre in extent, surrounded by a six-foot wall. Behind us there was a wide gateway through which our airplane had just come and across which workmen were dropping bars made of some material like cement. Before us, dotting this acre or so of plateau, were small, domed structures made of the same cement-like material. In the center of the plateau rose a larger domed building with a segment of its roof open to the stars and through this opening I could see the shadowy suggestion of a great lamp. There was the source of that powerful magnetic ray!

Foulet and Brice scrambled out and stood beside me. They said never a word, but I knew that every sense was alert.

“If you will follow me,” that same cold, expressionless voice murmured. I turned to look at the man. He was not bad looking, clean shaven, well tailored. He swung his eyes to meet my gaze and as he did so that same chill fled along my spine. His eyes--what was the matter with them? They were dark--brown or black--and as shiny as shoe buttons. But there was no gleam of expression in them. Their shine was the glitter of polished glass.

Without a word we followed him across the small cleared space where our airplane stood, past a row of the small, domed structures to a low door cut in the white wall of the great central building. At the doorway he turned.

“I am taking you to the Master,” he said; then, over his shoulder he added. “There is no means of escape--we are two thousand feet above the earth!” And he laughed--a quick, short cackle of crazy laughter. I felt the breath catch in my throat and the short hairs prickle at my neck. Foulet gripped my arm. Through my coat I could feel the chill of his fingers, but his grasp steadied me.

We walked on, following our guide. Down a narrow passageway, through a low arched door into a small room, evidently an ante-chamber to a larger room beyond. Without a word our guide left us, passing through another door which he closed after him.

Brice and Foulet and I exchanged looks, but we were silent. It might be we were watched. It might be that the very walls had ears. We could trust nothing.

Our guide returned. “The Master,” he said and flung open a wide door.

We found ourselves in a large room filled with paraphernalia of all sorts: wires, lights, laboratory tables cluttered with test tubes and apparatus--and in the midst of this ordered chaos stood a man, his gleaming eyes watching us fixedly.

At first I was conscious of nothing but his eyes. Large, coal black and shiny with that peculiar, expressionless gloss I had noted in the eyes of our guide. Later I realized that he was of slight build, meticulously neat, with a tiny black waxed mustache and a carefully trimmed Van Dyke beard.

“Welcome to my floating island,” he said gravely, never swerving those shiny eyes for an instant. “We have hoped long for your coming.” He paused, noiselessly rubbing his hands, and watching us. We stared back, fascinated by that glossy, fixed gaze. “There is much to tell you,” he went on, “and to ask you.” He permitted himself a slow smile that spread his lips but failed to reach his eyes. “During your stay here,” he continued, “which I hope will be both long and profitable, you will become my slaves and will know me as Master. But before you come under my domination you may know my name.”

For the first time he moved his eyes. His glance swept the room as if to assure himself we were alone. He stepped, as swiftly and softly as a cat, over to the door through which we had entered, opened it, spoke to our guide who was waiting in the ante-room, closed it and returned. He faced us, his lips smiling and his eyes as blank as polished agate.

“My name,” he said softly, “is Algernon--Frederick--Fraser!” He paused and watched us. Behind me I felt Foulet start; I heard Brice’s quickly suppressed gasp. My own throat closed on words that might have been fatal. Algernon Frederick Fraser! Was it possible? Could it be?

Five years before Fraser had suddenly burst on the world of science. He had made some amazing discoveries regarding the power of light; discoveries that would reorganize the living conditions of the world. For a week or two the papers were filled with the man’s amazing genius; then no more was heard of him. Had he died? What was the story?

Two years passed and even the name of Fraser was forgotten. Then suddenly it burst forth again in the headlines of the world. Fraser had disappeared! Fraser had vanished! But not as a brilliant genius of science; he had gone as an escaped lunatic! After his amazing burst of fame his mind snapped. Somehow the story had been kept out of the press.

Fraser was incarcerated in a quiet, very private asylum, and that was all. All--until he escaped. When that happened the story couldn’t be hushed any longer. The press was informed, the people were warned. He became known as the Mad Menace. The police and secret service organizations of the world searched for him. His name became a byword. Where had he gone? What would he do? What was his scheme? For he was still the astounding scientific genius. That portion of his mind was untouched. At the time of his escape the physicians in charge of the case assured the press that Fraser’s scientific mind was every bit as sound as ever.

And that was all. Aside from his god Science he was a maniac--inhuman, cruel, unreasoning. What would such a man do loosed in the world? What might he not do? Was it possible that it was this man who stood before us now with his eyes fastened upon us so intently and his lips spread in that little, empty smile? Suddenly I knew! Those eyes! Those eyes were the shiny, vacuous, soulless eyes of a madman!

“I see,” he said softly, “that you have heard of me. But it is three years since your world has seen me--yes?” He laughed--a low laugh that seemed to freeze the air around him. “They call me mad.” His smile faded, his eyes bored through us like steel needles. “I am not mad! No madman could do what I have done in three years!” For the first time an expression flickered in his eyes--a crafty gleam of vanity that flared instantaneously. “Would you like to see?” He leaned toward us. We bowed, but it was Brice who spoke.

“Very much, Doctor Fraser--”

“Don’t call me that!” The man whirled like a tiger ready to spring. “Don’t call me that! I am Master here! Call me Master! Say it.” His voice rose to a shriek. “Say it--Master!”

I clamped my teeth against the bloodless horror of that maniacal voice. It chilled my veins. Again I felt the hair rise on my scalp. Brice bowed quietly; and his eyes, serene and blue, met Fraser’s fairly.

“Of course, Master.” His low English voice soothed the bristling silence. “I am sure I speak for Monsieur Foulet and Lieutenant Ainslee when I say that we would be most deeply interested in your achievements.”

Fraser was placated. He relaxed. He softly rubbed his hands while a smug, crafty smile flitted across his lips. “You will follow me,” he murmured.

He led the way back through the ante-room and down the passageway till we stood again under the stars, and again I was struck by the strange light, warm and faint and rosy like a sunset afterglow. As if he read my thought Fraser turned to me.

“I will show you first the source of this rosy light; that, I believe, will explain a great deal.” He led the way down one of the narrow pathways between the low, domed houses--if they could be called houses, for they were little larger than kennels. At the six-foot wall that surrounded this plateau he paused. “Would you like to look over the wall?” he asked.

For the space of a breath we hesitated. Was this a trap? Through my mind flashed the words of the man who had guided us to Fraser. “You are two thousand feet above the earth,” he had said. Was that true? And if it were, might not Fraser push us over the wall? But instantly logic came to my rescue. Fraser had brought us here, and he could have brought us for but one thing: to question us. Would he be apt to do us harm before those questions were asked? And besides, would Fraser’s brilliantly subtle mind stoop so low as to destroy enemies by pushing them over a wall?

“Thank you,” we murmured simultaneously. “This whole achievement is of tremendous interest to us,” Foulet added.

Fraser chuckled. “It will be of greater interest--later,” he said, and his blank, glittering eyes rested on first one of us, then another with a cold, satisfied gleam. Then he lifted his hand and opened a square door in the wall about the size of a port-hole. To my surprise the little door swung back as lightly as a feather and made scarcely a sound as it slammed against the wall itself. Again Fraser answered my unspoken thought.

“It has only substance,” he said with his vain smirk. “No weight whatever. This entire platform together with its huts is lighter than air. If I should tear loose this little door it would float out of my hands instantly and go straight up to the stars. The substance--I have called it Fleotite--is not only lighter than air but lighter than ether.”

“But we are not floating,” said Brice; “we are stationary. Is the lightness of your Fleotite counteracted by the weight of the men and machines?”

Fraser shook his head. “Not entirely,” he said. “But first look through this little window. Then I will explain.”

Eagerly we pressed forward. Our danger was almost forgotten in our interest. This was amazing--stupendous! Together, shoulder to shoulder, we gazed through the aperture. We were suspended in space! Above us shone the blue-black Arabian night, and beneath us--far, far beneath--lay the sands of the desert looking rosy and warm in that same dull red glare of light that, to a fainter degree, gave us the effect of afterglow. But we were not floating; we were anchored as securely as a ship riding in a calm harbor.

We turned back to Fraser, amazed, awed, bursting with questions. Madman he might be, but he had wrought a miracle.

“I will explain,” he said and his eyes gleamed with pride. “Of course you know of my tremendous discoveries connected with the power of light. At any rate, five years ago, the scientific world on earth thought they were tremendous. In reality that was nothing to my amazing strides in the past three years. There is nothing that cannot be done with light! Nothing!” For the first time Fraser’s eyes became alive. They were illumined. His whole body seemed to radiate light and fire and genius. We listened, fascinated.

“Take, for instance,” he continued eagerly, “that ray with which I drew you and your plane to me. That ray is the pure power of magnetism. At full strength it will draw anything to it instantly. Fortunately the power can be regulated: I can switch a lever in my laboratory and draw things to me, via the ray, at any speed I wish--one hundred, two hundred, a thousand miles an hour.”

“How far can you throw the ray?” asked Foulet, and I knew he was thinking of that glider that rose from the roof-tops of Constantinople. Fraser also knew he was thinking of that.

“I did not draw the glider,” he said quietly. “The airplane I sent did that. My airplanes carry batteries of this ray. In the beginning I found gliders to be more practical for my purposes than airplanes. For one thing they were silent. My only problem was that of getting them off the ground. Once they were in the air I could manage everything. It was this problem that inspired this discovery and perfection of the ray. But, you asked how far I can throw the ray? This main lamp, that I operate myself from here, is effective at two hundred miles. At one hundred miles it enjoys its full power.”

“And you can draw anything to you,” asked Brice, “within the radius of the magnetic ray?”

“Anything in the air,” answered Fraser. “But of course I must use caution. Great caution. If I drew planes to me indiscriminately I would draw attention to myself; my secret and my location here would leak out. No. That must not be. So the only planes I bring are my own--and yours.” He paused and his black eyes, again glassy, swept over us. “It is a compliment I pay you,” he said finally. “You have become too troublesome. You know too much. Sooner or later the time would come when you would combine your forces. That would be a nuisance. So I decided to bring you here.”

“Suppose,” asked Foulet curiously, “we hadn’t fallen into your trap? Suppose we had turned back before reaching the point where your ray is effective?”

Fraser shook his head and that smug, offensive smile appeared again. “You were trapped from the beginning, though you didn’t know it,” he said. “The plane you were following was equipped with batteries of the ray which, while not as powerful as the lamp I have here, were still powerful enough to hold you to the course we choose you to run. But enough of the ray,” he added impatiently. “There are one or two other things I want to explain and then--” he paused and the pause, somehow, was alive with menace. What was he going to do after he had finished treating us as honored guests? For the third time he answered my unspoken question. His eyes narrowed till they were black, glittering slits. His voice, as he leaned toward us, was no more than a hissing whisper.

“Slaves!” he said, and his lips twisted. “How will you like to be slaves of Mad Algy Fraser?” He laughed--a chuckle that started in his throat and rose and rose till it seemed to shatter my ear-drums. I felt my teeth grinding together and my nails bit my palms in my effort to control my nerves against the strain of that maniacal glee. Suddenly he sobered. His laugh died instantly like a radio that had been snapped off. “Listen and I will tell you. I will tell you everything because it is necessary for you to know so that you may work for me intelligently and you will remember better and be of greater use to me if I tell you now while you are yet--sane!”