a Vorkulian
practice drill, the heptagons were destroying the hexan fleet. Seven
mighty green tractors would lash out, seize an attacking sphere, and
snap it into the center of mass of the unit of seven. There would be a
brief flash of dull red, a still briefer flare of incandescence, and the
impalpable magnets would leap out to seize another of the doomed globes.
It was only a matter of moments until not a hexan vessel remained; and
the Vorkulian juggernaut spiraled onward, now at full acceleration,
toward the hexan stronghold dimly visible far ahead of them--a vast
city built around Jupiter's northern pole.

At the controls of his projector, Kromodeor spun a dial with a
many-fingered, flexible hand and spoke.

"Wixill, I am being watched again--I can feel very plainly that strange
intelligence watching everything I do. Have the tracers located him?"

"No, they haven't been able to synchronize with his wave yet. Either
he is using a most minute pencil or, what is more probable, he is on a
frequency which we do not ordinarily use. However, I agree with you that
it is not a malignant intelligence. All of us have felt it, and none of
us senses enmity. Therefore, it is not a hexan--it may be one of those
strange creatures of the satellites, who are, of course, perfectly
harmless."

"Harmless, but unpleasant," returned Kromodeor. "When we get back I'm
going to find his beam myself and send a discharge along it that will
end his spying upon me. I do not...."

* * * * *

A wailing signal interrupted the conversation and every Vorkul in
the vast fleet coiled even more tightly about his bars, for the real
battle was about to begin. The city of the hexans lay before them,
all her gigantic forces mustered to repel the first real invasion of
her long and warlike history. Mile after mile it extended, an orderly
labyrinth of spherical buildings arranged in vast interlocking series
of concentric circles--a city of such size that only a small part of it
was visible, even to the infra-red vision of the Vorkulians. Apparently
the city was unprotected, having not even a wall. Outward from the low,
rounded houses of the city's edge there reached a wide and verdant
plain, which was separated from the jungle by a narrow moat of
shimmering liquid--a liquid of such dire potency that across it,
even those frightful growths could neither leap nor creep.

But as the Vorkulian phalanx approached--now shooti