Where did they go?" He was echoing Smithy's
questions and finding no ready answers. And that flame-thrower that
had cut down old Riley--how was that worked? Its one green flash had
been almost instantaneous.

He was puzzling over such futile questioning when he saw the first
sign of attack.

* * * * *

At the foot of the derrick was the hoisting shed. Except for that,
there was clear sand for a radius of fifty feet around the derrick's
base. Dean was staring suspiciously at that open space almost directly
underneath.

Moving sand! He hardly knew what he had seen at first. Then the sand
at one point bulged upward unmistakably.

For one instant Dean's thoughts shot off at a tangent. It was like the
work of a huge gopher--he had seen the little animals break through
like that. Then the sand parted, and something, indistinct, blurred,
dark against the yellow background, broke from cover.

Rawson swung the rifle's muzzle over and down. Below him the vague
shadow had moved. Dean caught the blurred mass beyond his sights, then
swung the weapon aside. Who was it? He would have a look first.

The thin crack of his rifle ripped the silence of the sleeping camp.
Dean had aimed to one side and he regretted it in the instant of
firing. For, in the same second, there had come from the moving shadow
the gleam of starlight reflected upward from polished metal.

* * * * *

Dean swung the rifle back. He fired quickly a second time. Beside him
the big light hissed into action and the whole camp sprang to sudden,
blazing light. And through the quick brilliance, more dazzling even
than the white glare itself, was one blinding line of green flame.

Dean saw it as it began. It came from the dim shadow that had sprung
suddenly into sharp outline as the big lights came on. He saw the
figure. He sensed that it was a man, though he knew vaguely that the
figure was grotesque and hideous in some manner he had no time to
discern.

The thin line of green flame ripped straight out, swinging in a quick,
sweeping trajectory, slashing through the steelwork of the great
derrick itself!

Dean knew he was lost in the blinding instant while that fiery jet was
sweeping in a fan-shaped sector of vivid green. A knife of flame! It
had destroyed a man: it was now cutting down a framework of steel as
well!

The derrick was falling as he fired again. There came a crushing jar
downward a