The ship, suddenly exposing its lights, was perfectly visible above us. Five thousand feet up, possibly. A tiny silver bird in the moonlight: but even with the naked eye I could see by its light pattern that it was the official Porto Rican patrol-liner. It saw us down here: recognized this bandit flyer, no doubt.

And it was coming down!

There was a confusion as the bandits rushed aboard. The patrol was dropping in a swift spiral. I watched tensely, holding Jetta, with the turmoil of the embarking bandits around me. Gutierrez stood with levelled weapon.

"They have not moved, Commander."

De Boer was here. The treasure was aboard.

"Ready, Hans. Lift us."

The landing portes clanged as they closed. Hans shoved at his switches. I heard the helicopter engines thumping. A vertical lift: there was no s.p.a.ce in this rocky defile for any horizontal take-away.

He was very calm, this De Boer. He sat in a chair at a control-bank of instruments unfamiliar to me.

"Full power, Hans: I tell you. Lift us!"

The ship was quivering. We lifted. The rocks of the gully dropped away. But the patrol-ship was directly over us. Was De Boer rushing into a collision?

"Now, forward, Hans."

We poised for the level flight. Did De Boer think he could out-distance this patrol-ship, the swiftest type of flyer in the Service? I knew that was impossible.

The silver ship overhead was circling, watchful. And as we levelled for forward flight it shot a warning searchlight beam down across our bow, ordering us to land.

De Boer laughed. "They think they have us!"

I saw his hand go to a switch. A warning siren resounded through our corridor, warning the bandits of De Boer's next move. But I did not know it then: the thing caught me unprepared.

De Boer flung another switch. My senses reeled. I heard Jetta cry out.

My arm about her tightened.

A moment of strange whirling unreality. The control room seemed fading about me. The tube-lights dimmed. A green glow took their place--a lurid sheen in which the cubby and the tense faces of De Boer and Hans showed with ghastly pallor. Everything was unreal. The voices of De Boer and Hans sounded with a strange tonelessness. Stripped of the timber that made one differ from the other. Hollow ghosts of human voices. By the sound I could not tell which was De Boer and which was Hans.

The corridor was dark; all the lights on the ship faded into this horrible dead green. The window beside me had a film on it. A dead, dark opening where moonlight had been. Then I realized that I was beginning to see through it once more. Starlight. Then the moonlight.

We had soared almost level with the descending patrol-ship. We went past it, a quarter of a mile away. Went past, and it did not follow.

It was still circling.

I knew then what had happened. And why this bandit ship had seemed of so strange an aspect. We were invisible! At four hundred yards, even in the moonlight, the patrol could not distinguish us. Only ten of these X-flyers were in existence: they were the closest secret of the U. S. Anti-War Department. No other government had them except in impractical imitations. I had never even seen one before.

But this bandit ship was one. And I recalled that a year ago, a suppressed dispatch intimated that the Service had lost one--wrecked in the Lowlands and never found.

So this was that lost invisible flyer? De Boer, using it for smuggling, with Perona and Sp.a.w.n as partners. And now, De Boer making away in it with Sp.a.w.n's treasure!

The bandit's hollow, toneless, unreal chuckle sounded in the gruesome lurid green of the control room.

"I think that surprised them!"

The tiny silver shape of the baffled local patrol-ship faded behind us as we flew northward over heavy, fantastic crags; far above the tiny twinkling lights of the village of Nareda--out over the sullen dark surface of the Nares Sea.

CHAPTER XIII

_The Flight to the Bandit Stronghold_

During this flight of some six hours--north, and then, I think, northeast--to the remote Lowland fastness where De Boer's base was located, I had no opportunity to learn much of the operation of this invisible flyer. But it was the one which had been lost. Wrecked, no doubt, and the small crew aboard it all killed. The vessel, however, was not greatly damaged: the crew were killed doubtless by escaping poisonous gases when the flyer struck.

How long it lay unfound, I cannot say. Perhaps, for days, it still maintained its invisibility, while the frantic planes of the U. S.

Anti-War Department tried in vain to locate it. And then, with its magnetic batteries exhausting themselves, it must have become visible.

Perona, making a solo flight upon Nareda business to Great London, came upon it. Perona, Sp.a.w.n and De Boer were then in the midst of their smuggling activities. They salvaged the vessel secretly. De Boer, with an incongruous flair for mechanical science, was enabled in his bandit camp, to recondition the flyer--building a workshop for the purpose, with money which Perona freely supplied.

Some of this I learned from De Boer, some is surmise: but I am sure it is close to the facts.

I have since had an opportunity--through my connection with this adventure which I am recording--of going aboard one of the X-flyers of the Anti-War Department, and seeing it in operation with its technical details explained to me. But since it is so important a Government secret, I cannot set it down here. The principles involved are complex: the postulates employed, and the mathematical formulae developing them in theory, are far too intricate for my understanding.

Yet the practical workings are simple indeed. Some of them were understood as far back as 1920 and '30, when that pioneer of modern astrophysics, Albert Einstein, first proved that a ray of light is deflected from its normal straight path when pa.s.sing through a magnetic field.

I am sorry that I cannot give here more than this vague hint of the workings of the fantastic invisible flyers which to-day are so often the subject of speculation by the general public which never has seen them, and perhaps never will. But I think, too, that a lengthy pedantic discourse here would be out of place. And tiring. After all, I am trying to tell only what happened to me in this adventure. And to little Jetta.

A very strangely capable fellow, this young De Boer. A modern pirate: no other age could have produced him. He did not spare Perona's money, that was obvious. From his hidden camp he must have made frequent visits to the great Highland centers, purchasing scientific equipment: until now, when his path crossed mine. I found him surrounded by most of the every-day devices of our modern world. The village of Nareda was primitive: backward. Save for its modern lights, a few local audiphones and image-finders, and its official etheric connections with other world capitals, it might have been a primitive Latin American village of a hundred years ago.

But not so De Boer's camp, which presently I was to see. Nor this, his flyer, with which his smuggling activities had puzzled Hanley's Office for so many months. There was nothing primitive here.

De Boer himself was a swaggering villain. I saw him now with his cloak discarded, in the normal tube-lights of the control room when, after a time, the mechanism of invisibility of the flyer was shut off. A fellow of six feet and a half at the very least, this De Boer. Heavy, yet with his great height and strength, lean and graceful. He wore a fabric shirt, with a wide-rolled collar. A wide belt of tanned hide, with lighters, a little electron drink-cooler and other nick-nackeries hanging from ta.s.seled cords--and a naked, ugly-looking knife blade clipped beside a holster which held an old-fashioned exploding projector of leaden steel-tipped bullets.

His trousers were of leather, wide-flaring, ending at his brawny bare knees, with wide-cut, limp leather boots flapping about his calves in ancient piratical fashion. They had flaring soles, these shoes, for walking upon the Lowland caked ooze. The uppers were useless: I rather think he wore them because they were picturesque. He was a handsome fellow, with rough-hewn features. A wide mouth, and very white, even teeth. A cruel mouth, when it went grim. But the smile was intriguing: I should think particularly so to women.

He had a way with him, this devil-may-care bandit. Strange mixture of a pirate of old and an outlaw of our modern world. With a sash at his waist, a red handkerchief about his forehead, and a b.l.o.o.d.y knife between his teeth. I could have fancied him a fabled pirate of the Spanish Main. A few hundred years ago when these dry Lowlands held the tossing seas. But I had seen him, so far, largely seated quietly in his chair at his instrument table, a cigarette dangling from his lips, and, instead of a red bandanna about his forehead, merely the elastic band holding the lens of his image-finder. It caught in the locks of his curly black hair. He pushed it askew; and then, since he did not need it now, discarded it altogether.

Where we went I could not surmise, except that we flew low over the sullen black waters of the Nares Sea and then headed northeast. We kept well below the zero-height, with the dark crags of the Lowlands pa.s.sing under us.

The night grew darker. Storm clouds obscured the moon; and it was then that De Boer shut off the mechanism of invisibility. The control room, with only the watchful Gutierrez now in it--besides De Boer, Jetta and myself--was silent and orderly. But there were sounds of roistering from down the ship's corridor. The bandits, with this treasure of the radiumized quicksilver ingots aboard, were already triumphantly celebrating.

I sat whispering with Jetta. De Boer, busy with charts and navigational instruments, ignored us, and Gutierrez, so long as we did not move, seemed not to object to our whispers.

The night slowly pa.s.sed. De Boer served us food, calling to one of his men to shove a slide before us. For himself, he merely drank his coffee and an alcoholic drink at his instrument table, while absorbed in his charts.

The roistering of the men grew louder. De Boer leaped to his feet, cursed them roundly, then went back to his calculations. He stood once before Jetta, regarding her with a strange, slow smile which made my heart pound. But he turned away in a moment.