showed on shore had vanished. There was an atmosphere of stark
abandonment and death which struck the Terrans forcibly.

Those pylons, Ross studied them. Something familiar in their
construction teased his memory. That refuel planet where the derelict
ship had set down twice, on the voyage out and on their return. That had
been a world of metal structures, and he believed he could trace a
kinship between his memory of those and these pylons. Surely they had no
connection with the earlier castle on the cliff.

Once more Ashe ducked to reset the probe. And in the fast-fading light
they watched a third and last picture. But now they might have been
looking at the island of the present, save that it bore no vegetation
and there was a rawness about it, a sharpness of rock outline now
vanished.

Those pylons, were they the key to the change which had come upon this
world? What were they? Who had set them there? For the last Ross thought
he had an answer. They were certainly the product of the galactic
empire. And the castle ... the ships ... natives ... settlers? Two
widely different eras, and the mystery still, lay between them. Would
they ever be able to bring the key to it out of time?

They swam for the shore where Ui had a fire blazing and their supper
prepared.

"How many years lying between those probes?" Ross pulled broiled fish
apart with his fingers.

"That first was ten thousand years ago, the second," Ashe paused, "only
two hundred years later."

"But"--Ross stared at his superior--"that means----"

"That there was a war or some drastic form of invasion, yes."

"You mean that the star people arrived and just took over this whole
planet?" Karara asked. "But why? And those pylons, what were they for?
How much later was that last picture?"

"Five hundred years."

"The pylons were gone, too, then," Ross commented. "But why--?" he
echoed Karara's question.

Ashe had taken up his notebook, but he did not open it. "I think"--there
was a sharp, grim note in his voice--"we had better find out."

"Put up a gate?"

Ashe broke all the previous rules of their service with his answer:

"Yes, a gate."

4

Storm Menace

"We have to know." Ashe leaned back against the crate they had just
emptied. "Something was done here--in two hundred years--and then, an
empty world."

"Pandora's box." Ross drew a hand across his forehead, smearing sweat
and fine sand into a brand.

Ashe nodded. "Maybe we run