The _Esperance_ swung about and headed back toward the island. The sea and the distant island looked comfortingly normal and beautiful in the sunshine. Under so blue a sky it did not seem reasonable to worry about anything. Events or schemes at the bottom of the sea seemed certainly the last things to be likely to matter to anyone. Terry had the _Esperance_ almost between the reefs before he tried the new contrivance. If it worked, it should be possible to make a relief map of the ocean bottom with every height and depth on the sea-bed plotted with precision. He started to operate the new instrument. First he traced the steep descent from the flanks of the submarine mountain whose tip was Thrawn Island. He traced them down to the abyss which was the Luzon Deep. Then he began to trace the ocean bottom at its extreme depth, on what should have been submarine plains at the foot of the submerged mountain. The instrument began to give extraordinary readings. The bottom, in a certain spot, read forty-five hundred fathoms down. But suddenly there was a reading of twenty-five hundred. There was a huge obstruction, twelve thousand feet above the bottom of the sea, more than twenty thousand feet below the surface. The instrument scanned the area. Something else was found eighteen hundred fathoms up. These were objects of enormous size, floating, or perhaps swimming in the blackness. They were not whales. Whales are air-breathers. They cannot stay too long in deep waters, motionless between the top and the bottom of the sea. The instrument picked up more and more such objects. Some were twenty-five hundred fathoms from the bottom, and two thousand from the surface. Some were twenty-two hundred up, and twenty-three hundred down. There were eighteen hundred-fathom readings, and twenty-one, and twenty-four, and nineteen. The readings were of objects bigger than whales. They rose very slowly, and appeared to rest, then rose some more, and rested.... Blank faces turned to Terry. He licked his lips and looked for Deirdre. Then he said evenly, "We go into the lagoon. And if we come out again--if!--we leave Deirdre ashore, unless these readings have been cleared up. There are chances I'm not willing to take." The _Esperance_ headed in. It was not possible for the new instrument to tell what the large objects were. They could be monstrous living creatures, perhaps squids, and one could only guess that their errand was to deal with the surface-creatures--men--who speared fish and giant squids and set off explosions in the Luzon Deep. Or the rising objects could be, say, bolides which had dived into the Deep from outer space and were now coming to the surface to make sure that the natives of the earth did not again disturb the depths taken over by beings from another planet. _Nine_