far back
in the cave.

"Wait," he told them. "I have a plan."

The creature vanished, and Harkness went cautiously forward to the
web. He took a detonite cartridge from his belt and placed it on the
floor close to the ropy strands. Another, and another, until he had a
close-packed circle of the deadly things. Then he placed a heavy,
metallic piece of rock beside them and proceeded, with infinite care,
to build a tower.

One irregular block upon another: it was like a child at play with his
toys. Only now the play was filled with deadly menace. The stones
swayed, then held in precarious, leaning uncertainty; the topmost was
directly above the cartridges on the floor.

"Back!" he ordered the others, "and lie flat on the floor. I must
guess at the amount of explosive for the job."

Chet and Diane were safe as Harkness weighed a fragment of metal in
his hand. One throw--and he must not hit the tower he had built....
The rock struck into the network of cords; he saw it clinging where it
struck, and saw the web shaking with the blow.

Over his shoulder, as he ran, he glimpsed the onrush of the beast.
Again the eyes were glaring, again the feelers were shaking furiously
at the web. They touched the leaning stones!

He had reached the place where Chet and Diane lay and saw the
beginning of the tower's fall; and in the split second of its falling
he threw himself across the body of the prostrate girl to shield her
from flying fragments of stone. A blast of air tore at him; his ears
were numbed with the thunder of the blast--a thunder that ended with a
crashing of stone on stone....

* * * * *

Slowly he recovered his breath; then raised himself to his feet to
look toward the entrance. It would be open now, the way cleared. But,
instead of sunlight, he saw utter dark. Where the mouth of the cave
had been was blackness--and nothing else!

He fumbled for his flash, and stood in despairing silence before what
the light disclosed.

The rock was black and shining about the mouth of the cavern. It had
split like glass. In shattered fragments it filled the forward part of
the cave. The whole roof must have fallen, and a crashing slide above
had covered all.

Chet was beside him; Harkness dared not look toward the girl coming
expectantly forward.

"We'll use more of the same," Chet suggested: "we will blast our way
out."

"And bring down more rock with each charge," Harkness told him
to