ed into
long, flat blades. They whirled in circles of light in the sun; and
the airplane beneath them poised, all but motionless, its main
propeller swinging idly, and then began slowly to drop downwards.

But Chris, swooping nearby, was still perplexed. Dropping down to
what? There was only the dense tropical growth beneath. He could see
no trace of men, no clearing, however small, no base--nothing but the
jungle.

"How in the dickens--" he began; and then stopped. At that moment the
jungle's secret was revealed.

* * * * *

As the helicopter-plane dropped to within a few hundred feet of it, a
strip of the sea verdure split in two and reared up. It looked, at
first, like magic. But from aloft Chris saw the trick and how the
camouflage was worked. What appeared to be a slice of the jungle roof
was, in reality, a metal framework cunningly plastered with layers of
green growth. An oblong, some fifty by a hundred feet, it parted in
the middle like a bridge that opens to let a steamer through,
revealing the lair of the plane.

Soon more was revealed. Two tiny, green-painted huts stood in the
minute clearing, and a few white-clad figures were by them, staring up
at the plane sinking down and at the other plane which soared above
like a buzzing mosquito.

One of the dwarfed figures in white waved an arm. The others around
him darted into the left-side hut. Then the helicopter-plane's wheels
touched the small space allotted for it in the clearing, and the
whirling propellers halted.

"So that's the secret!" Chris muttered. He pulled the microphone of
the radio-telephone to his lips and angled with the dials for
connection with the fleet hundreds of miles behind, meanwhile noting
his exact position on Azuero Peninsula. But before he spoke, some
sixth sense bade him glance below once more.

An icy shiver gripped his body.

A thin slit had appeared in the roof of the left-side hut. A spot of
bright blue light was winking evilly inside it. And, though he could
not hear it, Chris knew with terrible certainty that a shrill,
impatient whining was piercing from the machinery of a weapon inside
that hut--a weapon whose fangs had forked close to him once before--a
weapon which the winking eye of blue presaged.

It struck. But at the same instant Chris leaped desperately from the
cockpit of the scout.

* * * * *

He leaped almost into the teeth of the blue-tin