ts sheen, fading away to invisibility. He thought
he should be able, regardless of gleam or color, to see its outline;
but its outline, too, seemed to be becoming faint, indistinct.

* * * * *

Then, in a trice, it was gone, and a feeling of uneasiness, more
compelling than he had ever known before, coursed through the soul of
Sarka. Where had the cube gone? What was it? What was its purpose? He
tore his eyes away from the spot where he had last seen it, and stared
away to the shadow beneath the second nearest aircar, where he had
glimpsed another of the cubes.

The cube there, too, was fading out.

"Sarka! Sarka! Look!" came to his brain the thoughts of Jaska.

Sarka turned and stared at her, and a feeling of fear for which he
could not account at all took fast hold of him. The eyes of Jaska,
wide and staring as they had been when he commanded her to look away
from the cube under the aircar, were staring at that flat, table-like
rock, off to his right.

There, almost in the center of the rock, a gleaming something was
taking shape! Just a dull spot, in the center of the yellow glow; then
the beginning of the outline of a cube. Then, all at once, the cube
itself, gleaming and baleful!

Sarka gasped in terror. He had seen the cube vanish, its glow
disappear, and now here it was, almost close enough to touch, on a
rock beside him, gleaming and baleful as before! That it was the same
cube he had seen under the first aircar, he somehow knew without being
told. That it was a sentient _thing_ he also knew, for now there was
no mistaking the fact that, but for the presence in the little hollow
of Jaska and Sarka, the cube would not have moved.

* * * * *

Swift as light, Sarka's right hand darted to his belt, where his ray
director should be nestled against his need of it. And with his first
movement, the cube's brilliance vanished instantly, the cube
disappeared, and appeared again right before the face of Sarka, so
close he could touch it! Yet he did not turn the ray director against
it, nor did he extend his hand to touch the thing--because he was
afraid to do so!

Even as the cube appeared before his eyes, thrice baleful and menacing
in its close proximity, his eyes darted back to that broad flat rock,
where the second gleaming cube now appeared!

"Great God, Jaska!" he sent mentally, "what does it mean?"

"These," she answered bravely back, "are