An hour later, he was warily circling the spot where his little submarine was hidden. He pressed a button on a small device in his hand, and a signal was sent to the submarine. The various devices within it all responded properly. Nothing had been disturbed since the Nipe had set those devices weeks before. This was the touchiest part of any of his expeditions. There was always the chance, unlikely as it might be, that some one of the bipedal natives had found his machine. He dared not use it too close to his base because of the possibility of its drive vibrations being detected in the narrow estuary. Out here in the open sea there was far less likelihood of that, but leaving his submarine concealed out here increased the danger he exposed himself to every time he left his hidden nest. Satisfied that the machine was just as he had left it, he entered it and started its engines. He moved slowly and cautiously until he was well out to sea, well away from the continental shelf and over the ocean deeps. Then and only then did he accelerate to full cruising speed. * * * * * The full moon was in the west, hiding behind an array of low, scudding clouds, revealing its radiance in fitful bursts of silvery splendor that died again as another clotted cloud moved before the face of the white disk. The shifting light, shining through the breeze-tossed leaves of the palm trees on the beach below, made strange shadows on the sand, ever-changing patterns of gray and black on a background of white, moonlit sand. But the strangest shadow of all was one that did not change as the others did--a great centipede-like shape that seemed to wash slowly ashore on the receding tide. For a short while, it remained at the water's edge, apparently unmoving in the wash of the waves. Then, keeping low and balancing himself on his third pair of limbs, the Nipe moved in across the beach. The specially constructed sandals he wore left behind them a set of very human-looking footprints--prints that would remain unnoticed among the myriad of others that were already on the beach, left there by daytime bathers. It required more time yet to reach the city, and still more time to find the place he was looking for. It was almost dawn before he managed to find a storm sewer in which to hide for the day.