e metal vial and
dropped it into the trap. The heavy plug, a tiny duplicate of the exit
door, clicked shut upon it and spun, whining gently, into the opening.
Something clicked sharply, and one of the crew dropped a bar into place.
As it shot home, the Zenian in command of the crew pulled the release
plunger.

"Done, sir!" he said proudly.

I did not reply. My eye fixed upon the observation tube that was
following the tiny missile to the ground.

The Control City was directly below us. I lost sight of the vial almost
instantly, but the indicating cross-hairs showed me exactly where the
vial would strike; at a point approximately half way between the edge of
the city and the great squat pile of the administrating building, with
its gleaming glass penthouse--the laboratory in which, only a few
minutes before, I had witnessed the demonstration of the death which
awaited the Universe.

"Excellent!" I exclaimed. "Smartly done, men!" I turned and hurried to
the navigating room, where the most powerful of our television discs was
located.

The disc was not as perfect as those we have to-day; it was hooded to
keep out exterior light, which is not necessary with the later
instruments, and it was more unwieldy. However, it did its work, and did
it well, in the hands of an experienced operator.

With only a nod to Barry, I turned the range band to maximum, and
brought it swiftly to bear upon that portion of the city in which the
little vial had fallen. As I drew the focusing lever towards me, the
scene leaped at me through the clear, glowing glass disc.

* * * * *

Froth! Green, billowing froth that grew and boiled and spread
unceasingly. In places it reached high into the air, and it moved with
an eager, inner life that was somehow terrible and revolting. I moved
the range hand back, and the view seemed to drop away from me swiftly.

I could see the whole city now. All one side of it was covered with the
spreading green stain that moved and flowed so swiftly. Thousands of
tiny black figures were running in the streets, crowding away from the
awful danger that menaced them.

The green patch spread more swiftly always. When I had first seen it,
the edges were advancing as rapidly as a man could run; now they were
fairly racing, and the speed grew constantly.

A ship, two of them, three of them came darting from somewhere, towards
the administration building, with its glass cupola. I held