and the regular automatic action took place. A
tiny door slid open directly above in the dirigible's hull: a thin
ladder craned down--and Chris's nostrils caught a faint whiff of
something that cleared his mind of its confusion instantly.

Just a whiff, but it registered. Gas, with an odor resembling carbon
monoxide.

He stared up. Over the edge of the automatic trap-door above, a
white, contorted face was hanging. The dirigible swung; white-clad
shoulders and body slumped into view. Then, with a rush, the body
slipped through, jarred against the connecting ladder, slithered off
and went twisting and turning into the gulf below.

"God!"

Gassed! How, by what, Chris had no idea. A moment before he had been
about to follow the uncannily piloted plane; but now his duty was
plain. He knew with awful certainty that in minutes, seconds perhaps,
the giant ZX-1 was scheduled to roar into flames like its sister and
plunge into the Pacific.

He jerked out a gas mask. He was fitting it on with one hand as, with
the other, he hauled himself up the spider ladder into the hull of the
thundering, yawing dirigible.

He did not see, hovering a few hundred yards behind the ZX-1, the
mystery plane; he did not see it now begin to approach the rack once
more.

* * * * *

The crew of that dirigible of death, Chris discovered, had not had a
chance. White-clad bodies lay sprawled throughout the cabin which
contained the mechanism of the plane rack, stricken down silently at
their posts. There was no life, no sound save the booming of the
motors and the whip of the wind screaming past the uncontrolled air
titan.

But he did not pause there. He did not know what he was grappling
with--it seemed black magic--but he darted to a ladder which angled up
from the lowermost entrance cabin to the cat-walk that stretched from
the nose to the stern of the ship. If any infernal contrivance had
been planted aboard, it would be in the most vital spot.

Heart pumping from the artificial air he was breathing and from the
consciousness that each second might well be his last, he sprinted
along the interior gangway. Above was the vasty gloom of the gas bags
and the interweaving latticework of the supporting girders; the drum
of power-car motors and the strained creakings of cables and supports
echoed weirdly throughout. Outside was the sun and the sea and the
clean air, but this realm of mammoth shapes and dimness see