The Quabos were grim beings that were more intelligent than Aga's
fish-servants--even, she thought, more intelligent than humans
themselves. They had existed in their dark hole, as far as the Zyobites
knew, from the beginning of time.

Through the countless centuries they had constructed for themselves a
vast series of dens in the rock. There they had hidden away from the
deep-sea dangers. They, too, preyed on the mound-fish; but as there was
plenty of food for all, the Zyobites had never paid much attention to
them.

But--just before we had appeared, there had come about a subterranean
quake that changed the entire complexion of matters in Penguin Deep.

The earthquake wiped out the elaborately burrowed sea tunnels of the
Quabos, killing half of them at a blow and driving the rest out into the
unfriendly openness of the deep.

Now this was fatal to them. They were not used to physical self defense.
During the thousands of years of residence in their sheltered burrows
they had become utterly unable to exist when exposed to the primeval
dangers of the sea. It was as though the civilization-softened citizens
of New York should suddenly be set down in a howling wilderness with
nothing but their bare hands with which to contrive all the necessities
of a living.

* * * * *

Such was the situation at the time Stanley, the Professor and myself
arrived in Zyobor.

The Quabos must find an immediate haven or perish. On the ocean bottom
they were threatened by the mound-fish. In the higher levels they were
in danger from almost everything that swam: few things were so
defenceless as themselves after their long inertia.

Their answer was Zyobor. There, in perfect security, only to be reached
by the diving chamber that could be sealed at will by the twenty-yard,
counterbalanced lock, the Quabos would be even more protected than in
their former runways.

So--they were working day and night to invade Aga's city!

"But Aga," I interrupted impulsively at this point. "If these monsters
are fishes, how could they live here in air--"

I stopped as my objection answered itself before she could reply.

They would not have to live in air to inhabit Zyobor. They would
inundate the city--flood that peaceful, beautiful place with the awful
pressure of the lowest depths!

That thought, in turn, suggested to me that every building in Zyobor
would be swept flat if subjected suddenly to the rush of