, either to
imprison them, or to keep them under surveillance. Second--" He
hesitated.

Vye's own imagination supplied a second reason, a revolting one he
tried to deny to himself even as he put it into words:

"That broken spine--food...." Vye wanted Hume to contradict him, but
the Hunter only glanced around, his expression already sufficient
answer.

"Let's get out of here!" Vye was fighting down panic with every ounce
of control he could summon, trying not to bolt for the crevice. But he
knew he could not force himself any farther into that sinister valley.

"If we can!" Hume's words lingered direly in his ears.

Stones had smashed the globes by the river. If they still waited out
there Vye was willing to try and break them with his bare hands,
should escape demand such action. Hume must have agreed with those
thoughts, he was already taking long strides back to the cliff
entrance.

But that door was closed. Hume's foot, raised for the last step toward
the crevice corridor, struck an invisible obstruction. He reeled back,
clutching at Vye's shoulder.

"Something's there!"

The younger man put out his hand questingly. What his fingers
flattened against was not a tight, solid surface, but rather an unseen
elastic curtain which gave a little under his prodding and then drew
taut again.

Together they explored by touch what they could not see. The crevice
through which they had entered was now closed with a curtain they
could not pierce or break. Hume tried his ray tube. They watched thin
flame run up and down that invisible barrier, but not destroy it.

Hume relooped the tube. "Their trap is sprung."

"There may be another way out!" But Vye was already despondently sure
there was not. Those who had rigged this trap would leave no bolt
holes. But because they were human and refused to accept the
inevitable without a fight, the captives set off, not down into the
curve of the cup, but along its slope.

Tongues of brush and tree clumps brought about detours which forced
them slowly downward. They were well away from the crevice when Hume
halted, flung up a hand in silent warning. Vye listened, trying to
pick up the sound which had alarmed his companion.

It was as Vye strained to catch a betraying noise that he was first
conscious of what he did not hear. In the plains there had been
squeaking, humming, chitterings, the vocalizing of myriad grass
dwellers. Here, except for the sighing of the wind and a fe