About twenty miles away, in the lowest depression of Penguin Deep, lived a race of monsters which the people of Aga's city called Quabos. 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 the sea. The great low cavern, without the support of the myriad walls, would probably collapse--trapping the invading Quabos and leaving the rest without a home once more. But Aga answered this before I could voice it.