s an
underwater cliff about half a mile dead ahead. It rises to within four
thousand feet of the surface. And that thing out there is charging
straight into its base!"

"They must be aware of it," jerked the other. "See?--they've stopped!"

* * * * *

It was true. The gulf between the two colored spots was rapidly being
swallowed up. At a pulsing forty-one knots the _NX-1_ was closing in
on the motionless mystery craft.

"They're sinking to the floor itself," observed Wells. "Perhaps
waiting to attack."

The invisible beams from their ultra-violet light-beacons streamed
through the silent gloom outside, yet still the teleview screen was
empty. Keith punched a stud, and the _NX-1's_ whining motors dulled to
a scarcely audible purr.

"What is the thing?" muttered Hemmy Bowman. "God, Keith, what _is_
it?"

For answer, the commander dropped them the last five hundred feet. The
sea-floor rose like a gray ghost. More control studs were pushed; the
order-board below read: "All Power Off, Rest in Trim." The location
chart told a tale that wrung a gasp from Bowman's throat. The red and
green lights were practically touching....

The hands of Petty Officer Brown, the helmsman, were quivering on the
helm. Wells' fists kept tensing and relaxing as he peered for a sight
of the enemy in the teleview. Nothing showed but the moving fingers of
spectral kelp. Then both he and Bowman cried out as one:

"_There!_"

CHAPTER II

_The Silent Ray_

A strange shape had suddenly materialized on the screen--an immense,
oval-shaped thing of dull metal, with great curving cuts of glass-like
substance in its blunt bow, like staring eyes; a lifeless, staring
thing, stretching far into the curtain of gloom behind. How long it
was, Keith could not tell; at first his numb brain refused to grasp it
and reduce it to definite, sane standards of size and length. The cold
weeds of the sea-floor kelp beds swayed eerily over and around it.
From its bow, he saw, peculiar knobs jutted, the function of which he
guessed with dread.

Was it waiting with a purpose? Was it waiting--and inviting attack?

A frightened whisper from Hemmy Bowman broke the hush:

"Keith, the thing has ports, but shows no lights! What kind of
creatures can they be?"

As he spoke, the three men in the control room felt the unmistakable,
jarring tingle of an electric shock. And while their nerves still
jumped, it came again; and again.