s of terror.

"Note," he said to Jaska, "that there is a tiny trap-door in the
bottom of the aircar, and that the thing rests on a half-dozen of
those tentacles!"

"I see," came Jaska's reply.

Jaska went on:

"Note the gleaming thing on the ground, right below the aircar? I
wonder what it is?"

They studied the thing there, which seemed to be a huge jewel of some
sort that glittered balefully in the eery light of the Moon. It was,
perhaps, twice the size of an average man's torso, and was almost
exactly cubical in shape. As Sarka studied the thing, he sensed that
feeling flowed out of it--that the cube, whatever it was, was alive!

He tore his glance away from it, and realized that he accomplished the
feat with a distinct effort of will--as though the cube had willed to
hold his gaze, knew he was there. His eyes, peering around the inner
slope of the crater--which dipped over, some hundreds of feet down,
and plunged downward to some unknown depth--noted a broad, flat stone,
off to his right; and around the rim of the crater he counted a full
hundred of the aircars, all with their tentacles waving as if they
belonged to sentient creatures.

* * * * *

Below each one, as he studied them and strained his eyes to make out
details, he caught the baleful gleam of other cubes like the first he
had seen. The aircars, it seemed, were either sentinels, at the lip of
the crater, or were the dwelling places of sentinels--and the cubes
were those sentinels!

It seemed absurd, but it came to Sarka in a flash that that was the
answer, and his eyes came back to the first cube, because it was
nearer and more easy to study.

"I will not be swayed by the will of the thing," Sarka told himself.
"Nor will I allow it to analyze me! Jaska, do you do likewise!"

Beside him, Jaska shivered. He turned to look at her. Her face was
coldly white, and her eyes were big with terror and fascination as she
stared at that first cube, resting so balefully there under the first
aircar.

He shook her, and she seemed to bring her eyes to his with a terrific,
will-straining effort.

"Look at me!" he told her, telepathically. "Keep your eyes on me, for
to look at the cube spells danger!"

But his own eyes went back to the thing, and he studied it closely. A
cold chill raced through his body as he noted that its gleam was
becoming dull, fading slowly out. It had gleamed brightly at first,
and now was losing i