They met many people as they walked through the avenues of ageless trees and over the dwarf perennial grass that never needed trimming. After a while they grew tired of acknowledging greetings, for everyone knew Alvin and almost everyone knew the Keeper of the Records. So they left the paths and wandered through quiet byways almost overshadowed by trees. Sometimes the trunks crowded so closely round them that the great towers of the city were hidden from sight, and for a little while Alvin could imagine he was in the ancient world of which he had so often dreamed.

             The Tomb of Yarlan Zey was the only building in the Park. An avenue of the eternal trees led up the low hill on which it stood, its rose-pink columns gleaming in the sunlight. The roof was open to the sky, and the single chamber was paved with great slabs of apparently natural stone. But for geological ages human feet had crossed and recrossed that floor and left no trace upon its inconceivably stubborn material. Alvin and Rorden walked slowly into the chamber, until they came face to face with the statue of Yarlan Zey.

             The creator of the great Park sat with slightly downcast eyes, as if examining the plans spread across his knees. His face wore that curiously elusive expression that had baffled the world for so many generations. Some had dismissed it as no more than a whim of the artist's, but to others it seemed that Yarlan Zey was smiling at some secret jest. Now Alvin knew that they had been correct.

             Rorden was standing motionless before the statue, as if seeing it for the first time in life. Presently he walked back a few yards and began to examine the great flagstones.

             "What are you doing?" asked Alvin.

             "Employing a little logic and a great deal of intuition," replied Rorden. He refused to say any more, and Alvin resumed his examination of the statue. He was still doing this when a faint sound behind him attracted his attention. Rorden, his face wreathed in smiles, was slowly sinking into the floor. He began to laugh at the boy's expression.

             "I think I know how to reverse this," he said as he disappeared. "If I don't come up immediately, you'll have to pull me out with a gravity polarizer. But I don't think it will be necessary."

             The last words were muffled, and, rushing to the edge of the rectangular pit, Alvin saw that his friend was already many feet below the surface. Even as he watched, the shaft deepened swiftly until Rorden had dwindled to a speck no longer recognizable as a human being. Then, to Alvin's relief, the far-off rectangle of light began to expand and the pit shortened until Rorden was standing beside him once more.

             For a moment there was a profound silence. Then Rorden smiled and began to speak.

             "Logic," he said, "can do wonders if it has something to work upon. This building is so simple that it couldn't conceal anything, and the only possible secret exit must be through the floor. I argued that it would be marked in some way, so I searched until I found a slab that differed from all the rest."

             Alvin bent down and examined the floor.

             "But it's just the same as all the others!" he protested.

             Rorden put his hands on the boy's shoulders and turned him round until he was looking toward the statue. For a moment Alvin stared at it intently. Then he slowly nodded his head.

             "I see," he whispered. "So that is the secret of Yarlan Zey!"

             The eyes of the statue were fixed upon the floor at his feet. There was no mistake. Alvin moved to the next slab, and found that Yarlan Zey was no longer looking toward him.

             "Not one person in a thousand would ever notice that unless they were looking for it," said Rorden, "and even then, it would mean nothing to them. At first I felt rather foolish myself, standing on that slab and going through different combinations of control thoughts. Luckily the circuits must be fairly tolerant, and the code thought turned out to be 'Alaine of Lyndar.' I tried 'Yarlan Zey' at first, but it wouldn't work, as I might have guessed. Too many people would have operated the machine by accident if that trigger thought had been used."

             "It sounds very simple," admitted Alvin, "but I don't think I would have found it in a thousand years. Is that how the Associators work?"

             Rorden laughed.

             "Perhaps," he said. "I sometimes reach the answer before they do, but they always reach it." He paused for a moment. "We'll have to leave the shaft open: no one is likely to fall down it."

             As they sank smoothly into the earth, the rectangle of sky dwindled until it seemed very small and far away. The shaft was lit by a phosphorescence that was part of the walls, and seemed to be at least a thousand feet deep. The walls were perfectly smooth and gave no indication of the machinery that had lowered them.

             The doorway at the bottom of the shaft opened automatically as they stepped toward it. A few paces took them through the short corridor—and then they were standing, overawed by its immensity, in a great circular cavern whose walls came together in a graceful, sweeping curve three hundred feet above their heads. The column against which they were standing seemed too slender to support the hundreds of feet of rock above it. Then Alvin noticed that it did not seem an integral part of the chamber at all, but was clearly of much later construction. Rorden had come to the same conclusion.

             "This column," he said, "was built simply to house the shaft down which we came. We were right about the moving ways—they all lead into this place."

             Alvin had noticed, without realizing what they were, the great tunnels that pierced the circumference of the chamber. He could see that they sloped gently upward, and now he recognized the familiar gray surface of the moving ways. Here, far beneath the heart of the city, converged the wonderful transport system that carried all the traffic of Diaspar. But these were only the severed stumps of the great roadways: the strange material that gave them life was now frozen into immobility.

             Alvin began to walk toward the nearest of the tunnels. He had gone only a few paces when he realized that something was happening to the ground beneath his feet. It was becoming transparent. A few more yards, and he seemed to be standing in midair without any visible support. He stopped and stared down into the void beneath.

             "Rorden!" he called. "Come and look at this!"

             The other joined him, and together they gazed at the marvel beneath their feet. Faintly visible, at an indefinite depth, lay an enormous map—a great network of lines converging toward a spot beneath the central shaft. At first it seemed a confused maze, but after a while Alvin was able to grasp its main outlines. As usual, he had scarcely begun his own analysis before Rorden had finished his.

             "The whole of this floor must have been transparent once," said the Keeper of the Records. "When this chamber was sealed and the shaft built, the engineers must have done something to make the center opaque. Do you understand what it is, Alvin?"

             "I think so," replied the boy. "It's a map of the transport system, and those little circles must be the other cities of Earth. I can just see names beside them, but they're too faint to read."

             "There must have been some form of internal illumination once," said Rorden absently. He was looking toward the walls of the chamber.