Through the aeons, as they advanced along their different roads, the gulf between Lys and the cities widened. It was bridged only in times of great crisis; when the Moon was falling its destruction was carried out by the scientists of Lys. So also was the defense of Earth against the Invaders, who were held at bay in the final Battle of Shalmirane.

That great ordeal exhausted mankind; one by one the cities died and the desert rolled over them. As the population fell, humanity began the migration that was to make Diaspar the last and greatest of all cities.

Most of these changes did not affect Lys, but it had its own battle to fight-the battle against the desert. The natural barrier of the mountains was not enough, and many ages passed before the great oasis was made secure. The picture was blurred here, perhaps deliberately. Alvin could not see what had been done to give Lys the virtual eternity that Diaspar had achieved.

The voice of Seranis seemed to come to him from a great distance-yet it was not her voice alone, for it was merged into a symphony of words, as though many other tongues were chanting in unison with hers.

«That, very briefly, is our history. You will see that even in the Dawn Ages we had little to do with the cities, though their people often came into our land. We never hindered them, for many of our greatest men came from outside, but when the cities were dying we did not wish to be involved in their downfall. With the ending of air transport there was only one way into Lys-the carrier system from Diaspar. It was closed at your end, when the park was built-and you forgot us, though we have never forgotten you.

«Diaspar has surprised us. We expected it to go the way of all other cities, but instead it has achieved a stable culture that may last as long as Earth. It is not a culture that we admire yet we are glad that those who wish to escape have been able to do so. More than you might think have made the journey, and they have almost always been outstanding men who brought something of value with them when they came to Lys.»

The voice faded; the paralysis of Alvin’s senses ebbed away and he was himself again. He saw with astonishment that the sun had fallen far below the trees and that the eastern sky already held a hint of night. Somewhere a great bell vibrated with a throbbing boom that pulsed slowly into silence, leaving the air tense with mystery and premonition. Alvin found himself trembling slightly, not with the first touch of the evening’s chill, but through sheer awe and wonder at all that he had learned. It was very late, and he was far from home. He had a sudden need to see his friends again, and to be among the familiar sights and scenes of Diaspar.

«I must return,» he said. «Khedron-my parents-they will be expecting me.»

That was not wholly true; Khedron would certainly be wondering what had happened to him, but as far as Alvin was aware no one else knew that he had left Diaspar. He could not have explained the reason for this mild deceit, and was slightly ashamed of himself as soon as he had uttered the words.

Seranis looked at him thoughtfully.

«I am afraid it is not as easy as that,» she said.

«What do you mean?» asked Alvin. «Won’t the carrier that brought me here take me back again?» He still refused to face the idea that he might be held in Lys against his will, though the idea had briefly crossed his mind.

For the first time, Seranis seemed slightly ill at ease.

«We have been talking about you,» she said-not explaining who the «we» might be, nor exactly how they had consulted together. «If you return to Diaspar, the whole city will know about us. Even if you promise to say nothing, you would find it impossible to keep our secret.»

«Why should you wish it kept?» asked Alvin. «Surely it would be a good thing for both our peoples if they could meet again.»

Seranis looked displeased.

«We do not think so,» she said. «If the gates were opened, our land would be flooded with the idly curious and the sensation seekers. As it is now, only the best of your people have ever reached us.»

This reply radiated so much unconscious superiority, yet was based on such false assumptions, that Alvin felt his annoyance quite eclipse his alarm.

«That isn’t true,» he said flatly. «I do not believe you would find another person in Diaspar who could leave the city, even if he wanted to-even if he knew that there was somewhere to go. If you let me return, it would make no difference to Lys.»

«It is not my decision,» explained Seranis, «and you underestimate the powers of the mind if you think that the barriers that keep your people inside their city can never be broken.

However, we do not wish to hold you here against your will, but if you return to Diaspar we must erase all memories of Lys from your mind.» She hesitated for a moment. «This has never risen before; all your predecessors came here to stay.»

Here was a choice that Alvin refused to accept. He wanted to explore Lys, to learn all its secrets, to discover the ways in which it differed from his own home, but equally he was determined to return to Diaspar, so that he could prove to his friends that he had been no idle dreamer. He could not understand the reasons prompting this desire for secrecy; even if he had, it would not have made any difference in his behavior.

He realized that he must play for time or else convince Seranis that what she asked him was impossible.

«Khedron knows where I am,» he said. «You cannot erase his memories.»

Seranis smiled. It was a pleasant smile, and one that in any other circumstances would have been friendly enough. But behind it Alvin glimpsed, for the first time, the presence of overwhelming and implacable power.

«You underestimate us, Alvin,» she replied. «That would be very easy. I can reach Diaspar more quickly than I can cross Lys. Other men have come here before, and some of them told their friends where they were going. Yet those friends forgot them, and they vanished from the history of Diaspar.»

Alvin had been foolish to ignore this possibility, though it was obvious, now that Seranis had pointed it out. He wondered how many times, in the millions of years since the two cultures were separated, men from Lys had gone into Diaspar in order to preserve their jealously guarded secret. And he wondered just how extensive were the mental powers which these strange people. possessed and did not hesitate to use.

Was it safe to make any plans at all? Seranis had promised that she would not read his mind without his consent, but he wondered if there might be circumstances in which that promise would not be kept.

«Surely,» he said, «you don’t expect me to make the decision at once. Cannot I see something of your country before I make my choice?»

«Of course,» replied Seranis. «You can stay here as long as you wish, and still return to Diaspar eventually if you change your mind. But if you can decide within the nekt few days, it will be very much easier. You do not want your friends to be worried, and the longer you are missing the harder it will be for us to make the necessary adjustments.»

Alvin could appreciate that; he would like to know just what those «adjustments» were. Presumably someone from Lys would contact Khedron-without the Jester ever being aware of it-and tamper with his mind. The fact of Alvins disappearance could not be concealed, but the information that he and Khedron had discovered could be obliterated. As the ages passed, Alvin’s name would join those of the other Uniques who had mysteriously vanished without trace and had then been forgotten.

There were many mysteries here, and he seemed no closer to solving any of them. Was there any purpose behind the curious, one-sided relationship between Lys and Diaspar, or was it merely a historical accident? Who and what were the Uniques, and if the people from Lys could enter Diaspar, why had they not canceled the memory circuits that held the clue to their existence? Perhaps that was the only question to which Alvin could give a plausible answer. The Central Computer might be too stubborn an opponent to tackle, and would hardly be affected by even the most advanced of mental techniques.