is soon as I get there. Keep listening. Okay? Right;
signing off."

Silence, then, between the scout and the flagship far behind....

* * * * *

On--on Time passed. The scout's gas was down below the half-way mark.
They had covered two hundred miles now at a speed just bordering three
hundred. The plane ahead looked uncanny with its apparently empty
cockpit, but Chris could see all too well that death was pressing at
its invisible pilot. The big machine was literally staggering in its
course as the hands on its control stick grew weaker; was yawing
wildly, even as the ZX-1 had yawed after her crew had been slain by
vapors they could not see.

"He's got to last out!" Chris muttered. "Got to!"

At that moment land appeared, and the fleeing plane altered its
northeast course to due east with an abrupt jerk.

First it was a mere hazy line on the horizon; then it rose to a thrust
of land, jutted with cloud-misted hill-tops. Then, as the two roaring
specks that were airplanes came closer, heavy tropical foliage became
distinct, and white slashes of surf breaking on the shore. This was
the Azuero Peninsula, most western point of the Republic of Panama.

Aside from one small cluster of wretched huts, it was practically
uninhabited. Guarded by dense growth, only one or two of the dusty
paths which passed for roads wandered aimlessly through its tangled
creepers, trees and bush. To the southeast was the broad Gulf of
Panama, doorway to the Canal; on the other sides this thumb of land
was surrounded by the reaches of the Pacific.

The plane was obviously nearing its eyrie--dropping lower and lower,
losing speed and altitude; and also threatening each moment to tumble
down out of control into the smothering welter of olive-green below,
with a dead, unseen body in its cockpit.

But where was the landing field? They were now over the very heart of
the Peninsula, and still Chris, searching through his telescopic
sight, could see nothing but the monotonous roll of jungle. They must
come to it soon, or be over to the Caribbean Sea and the Mosquito
Gulf.

Then suddenly he started forward, staring. Of course there was no
landing field in sight. The mystery plane needed none. It possessed
the power of the helicopter: it could rise straight up or sink
straight down.

From each one of the two knob-like projections on its upper wing that
had puzzled him previously, a propeller had risen and unfold