On two occasions, once during the early afternoon, again near dusk, he had deliberately scraped the wall with a broken-off branch. Each time he had scurried back to the cover of the woods to watch the robots. Each time he had barely reached the first line of trees before the guards appeared. They made no attempt to leave the wall and gave no sign of having seen him. Watching their impersonal inspection bitterly, he thought about the wall. It did more than keep out unauthorized persons and screen from the curious the activities in the camp. Walls worked two ways. While Freemen blissfully pursued their endless pleasure, the wall made their camp a prison. Waiting for total darkness, Hendley let his reflections range beyond the wall to the bleak prospect of the endless desert. Would he find food and water in that wasteland? Would he lose himself in its vastness without ever finding his way to the nearest city? Angrily he brushed aside his doubts. Frightening as the desert might be, it could be no more terrible than a meaningless freedom. In the last light Hendley made his preparations, stripping leaves and thin useless branches from the long slender trunk of a fallen sapling he had found earlier in the day. He doubted that this rude pole-ladder would reach all the way to the top of the wall, but it would bring him close enough. He would have to clamber up in frantic seconds. And if he failed, there might be no second chance. At last he was ready. The darkness was deep. He crept to the edge of the woods, dragging his improvised ladder. For several minutes he crouched motionless, searching the wall. Something had disturbed his eye. Not movement, but a sense of something foreign in the darkness, a shape.... He went cold. Directly opposite his position, immobile on top of the wall, sat a robot-guard. Against the night sky its gray shape was almost invisible. How long had it been there? It must have come while he was busy cleaning off the tree trunk. But surely its station opposite him was a coincidence. Stealthily Hendley retreated into the woods, taking great pains to pull his pole-ladder silently through the undergrowth. Not until he had covered an estimated fifty yards to the left of his original position did he angle again toward the edge of the woods facing the wall. This was still too close, but it would give him a check against the tactics of the robot wall patrol. He had to know how many of them were on guard, and how they functioned. Reaching the cleared strip, he peered toward the wall. A robot--silent, impassive, tirelessly observant--sat exactly across the way.