to the water of the central
lagoon and into the air over it a flood of deadly vapor. As the Nevian
turned toward the prisoner there was an almost inaudible hiss and a tiny
jet of the frightful, outlawed stuff struck his open gills, just below
his huge, conical head. He tensed momentarily, twitched convulsively
just once, and fell motionless to the floor. And outside, the streams of
avidly soluble liquefied gas rushed out into air and into water. It
spread, dissolved, and diffused with the extreme mobility which is one
of its characteristics; and as it diffused and was borne outward the
Nevians in their massed hundreds died. Died not knowing what killed
them, not knowing even that they died. Costigan, bitterly resentful of
the inhuman treatment accorded the three and fiercely anxious for the
success of his plan of escape, held his breath and, grimly alert,
watched the amphibians die. When he could see no more motion anywhere he
donned his gas-mask, strapped upon his back a large canister of the
poison--his capacious pockets were already full of smaller
containers--and two savagely exultant sentences escaped him.

"I am a poor, ignorant specimen of ape that can be let play with
apparatus, am I?" he rasped, as he picked up the key tube of the
specialist and opened the door of his prison. "They'll learn now that it
ain't safe to judge by the looks of a flea how far he can jump!"

He stepped out through the opening into the water, and, burdened as he
was, made shift to swim to the nearest ramp. Up it he ran, toward a main
corridor. But ahead of him there was wafted a breath of dread Vee-Two,
and where that breath went, went also unconsciousness--an
unconsciousness which would deepen gradually into permanent oblivion
save for the prompt intervention of one who possessed, not only the
necessary antidote, but the equally important knowledge of exactly how
to use it. Upon the floor of that corridor were strewn Nevians, who had
dropped in their tracks. Past or over their bodies Costigan strode,
pausing only to direct a jet of lethal vapor into whatever branching
corridor or open door caught his eye. He was going to the intake of the
city's ventilation plant, and no unmasked creature dependent for life
upon oxygen could bar his path. He reached the intake, tore the canister
from his back, and released its full, vast volume of horrid contents
into the primary air stream of the entire city.

And all throughout that doomed city Nev