nother 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 Spawn as partners. And now, De Boer making
away in it with Spawn'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 wh