Raf was two streets away from the circling box but still able to keep it in sight when its easy glide stopped, and, in a straight line, it swooped toward a roof emitting a shrill, rising whistle. It rose again a few seconds later as if baffled, but it continued to hover at that point, keening forth its warning. The pilot reached the next building, but a street still kept him away from the conical structure above which the box now hung. Undecided, he stayed where he was. Should he go down to street level and investigate? Before he had quite made up his mind he saw the foremost of the alien scouting party round into the thoroughfare below and move purposefully at the cone tower, weapons to the fore. Judging by their attitude, the box had run to earth there the prey they had been searching for. But it wasn't to be so easy. With another eerie howl the machine soared once more and bobbed completely over the cone to the street which must lie beyond it. Raf knew that he could not miss the end of the chase and started on a detour along the roof tops which should bring him to a vantage point. By the time he had made that journey he found himself on a warehouse roof which projected over the edge of the river. From a point farther downstream a small boat was putting out. Two of the aliens paddled while a third crouched in the bow. A second party was picking its way along the bank some distance away, both groups seemingly heading toward a point a building or two to the left of the one where Raf had taken cover. He heard the shrilling of the box, saw it bobbing along a line toward the river. But in that direction there was only a mass of green. The end to the weird chase came so suddenly that he was not prepared, and it was over before he caught a good look at the quarry. Something moved down on the river bank and in that same instant the box hurtled earthward as might a spear. It struck, and the creature who had just crawled out--out of the ground as far as Raf could see--toppled into the stream. As the waters closed over the body, the box slued around and came to rest on the bank. The party in the boat sent their small craft flying toward the spot where the crawler had sunk. One of the paddlers abandoned his post and slipped over the side, diving into the oily water. He made two tries before he was successful and came to the surface with the other in tow. They did not try to heave the unconscious captive into the boat, merely kept the lolling head above water as they turned downstream once more and vanished from Raf's sight around the end of a pier, while the second party on the bank reclaimed the now quiet box and went off.