At this point a strange thing happened. As he lay there on the couch, listening to the singing and the crackling of the fire, he felt himself drifting into sleep. It was then that he realized that his "earlier self" must have fallen asleep at about this point, and that he had been witnessing that drift into the twilight world between sleep and waking. And now he was fascinated to observe the blurred images that wandered like slow clouds before his inner vision, and the alien voices that uttered meaningless yet strangely significant phrases -- one of them said: "His greenness will be more obstinate when he finds his tail." Then the voices seemed to turn into water which seeped into the cracks of his unconscious mind and ran into some underground lake of darkness. The effect was so strange that it made him feel sick and dizzy, as if everything had become unreal. He groped for the "off" button of the control unit, and felt a flood of relief as the normal world returned like daylight after a nightmare.

His curiosity about the control unit still strong, he touched the final button of the bottom row, which was labeled "20." The result was as unexpected as it was unpleasant.

He was suddenly gripped by a convulsion of sorrow and misery that struck with the unexpectedness of a summer storm or a violent blow. He was standing in the entrance to the burrow, looking down at a hideously swollen corpse which he could just recognize as that of his father. The face was black and the open eyes were bulging. The arm, wearing a copper bracelet, was flung up as if to protect the face from the fangs of an angry spider.

The old man's voice said: "I think that perhaps you should switch off the machine."

He was standing again by the couch. Niall's energies had been so drained by the shock that it cost him an effort of will to press the "off" button. He said: "Why did it do that?" Even his lips felt numb.

"The electrical pulses of the internalizer cause memory circuits to discharge. You selected a frequency connected with traumatic memories."

"But what good is it?" He knew the question was irrational, but the shock was turning to anger.

"Far more than you think." The old man's voice was so calm and reasonable that his anger evaporated. "I would advise you to repeat the experience."

"Why?" Niall's faith in the Steegmaster was implicit, but the idea appalled him.

"Because it will make the pain disappear. Try it." Bracing himself as if for a blow, Niall switched on the unit, then pressed the button labeled "20." Again he was assailed by waves of misery as he looked at his father's distorted face; this time he even noticed the puncture marks on the underside of the arm where the spider had injected the poison. Yet he was also aware that the misery was being experienced by the Niall who was standing in the entrance to the burrow, and that he himself was feeling it at second hand.

"Again." The old man's voice actually sounded sympathetic. As he pressed the button, and the memory returned to the beginning, he was even more clearly aware of the gap between his present and his past self. When that past self had experienced a sense of numbness, it had been a defense against an overwhelming surge of emotion; now the emotion had lost some of its power, Niall ceased to experience the numbness. Instead, he experienced rage and pity, and a sense of the futility of his father's death. "Again."

This time, even the rage and pity had lost their force.

"Again."

This time he felt only pity.

"Again."

The pity became a sense of sadness mingled with futile regrets.

"Again."

Now he could see that even regret and sadness were pointless; it had happened, and there was nothing he could do about it.

"Again."

Niall shook his head. "There's no need to do it again." He felt curiously calm and peaceful; he was also experiencing an odd sensation, as if he was growing physically older second by second. He asked: "How did the machine do that?"

"It didn't. Your own mind did it. Any negative emotion can be erased by reliving it."

To his surprise, he found himself yawning. The sense of shock had given way to a pleasant feeling of relaxation. But his brain felt tired, with the kind of fatigue he had experienced after making too much use of the thought mirror. He closed his eyes for a moment, tempted to fall asleep, then remembered why he was there, and forced himself back into wakefulness.

"You said I could learn about Skorbo's killers." "You wish to make the attempt now?"

"Yes, if it's possible."

"It is possible, but perhaps not entirely advisable. You need more practice with the internalizer. I would suggest at least another day."

Niall shook his head. "There's not time. One of them may still be in the city, and he could be gone by tomorrow."

"It is your choice. You understand the dangers."

He asked with misgiving: "Dangers?"

"You have already encountered the worst of them. Negative emotions."

"The worst?" He could not keep a note of relief out of his voice.

"You should not underestimate negative emotion." There was a hint of reproof in his tone.

"Of course. But if you don't object. . ."

"It is not for me to object or approve."

Again Niall had to remind himself that Steeg was a computer, not a human being.

"Then tell me what I have to do."

"First of all, concentrate upon this man. Try to envisage him clearly. It may help you to hold the pendant in your hand. Then, when you are ready, press number two, which induces the alpha state, then number nine, which amplifies short-term memory -- the experiences of the past few hours. You may then begin to receive impressions. If this fails, try deepening the alpha state."

Niall took the pendant from his pocket and held it in his right hand. But this seemed pointless; after all, he could not see it while he was holding it. Instead, he placed the chain round his neck, so the pendant rested on his chest. Then he touched the second button. The dreamy sensation returned, accompanied by a feeling that was like falling backwards. Now he closed his eyes, and envisaged the face of the dead man, with its large eyes, beaklike nose, and weak chin. For a moment it was real; then it became blurred. Even in the hour since he had seen it, the memory had faded, overlaid by other impressions. The more he tried to visualize it precisely, the less clear it became. He opened his eyes and touched the ninth button. The result was startling. He was again standing in the rubble-strewn corridor, smelling its distinctive odor of damp plaster and dust, and looking into the strange, dark eyes. He braced himself, knowing what was about to happen. There was the sensation of being struck violently in the face, while at the same time, his breathing was cut off as if someone had gripped his windpipe. His senses blurred, and everything seemed to go into slow motion. Yet because he was also observing it all from a distance, he also continued to stare into the face of his attacker, and to observe its expression of uncertainty and anxiety. He even experienced a flash of sympathy: this man was alone in a hostile city, surrounded by enemies. His safety depended on not being recognized, and now that he had been recognized, he had ceased to be the hunter, and became the quarry. . .

Over the man's shoulder, Niall saw the glue spider lowering itself silently out of its hole in the ceiling. The man heard it as its feet touched the floor, and started to turn.

Before he could do so, he was struck by the will power of the spider and immobilized; moments later, he was being held down on the floor by the spider's front legs, and a fine spray of glue was being squirted into his face. At the same time, Niall's vision cleared, and he became aware that Simeon was bending over him and helping him to his feet. He knew what would happen next, and the thought sickened him. Even as he was pressing the "off" button, the man was leaping to his feet and reaching for the knife hidden inside his garment; then, like a light being extinguished, he vanished.

The old man said: "You learned what you wanted to know?"

"No."

"What happened?"

"The man was about to commit suicide, and I didn't want to see it."

"I see."

The calm, level voice made him feel ashamed of himself. In the silence that followed, he said: "I'll try again."

"One moment." Niall paused, his finger on the control. "Every time you do this, you use up mental energy. The more tired you become, the less you are likely to discover -- the tired mind is unobservant."

Niall knew he was right; his brain was feeling heavy and dull. "I'll try just once more."

"Very well. But a word of advice. The longer you hold down the second control, the deeper the alpha state. This will increase your sensitivity. But it will also make you more vulnerable. I would suggest that you keep your finger on the off control."

"Thanks. I will."

He closed his eyes and made his mind a blank, deliberately inducing relaxation.

Then he pressed the "on" switch and touched the second button. The dreamy sense of unreality was a little like sinking into a sea of some soft, silky material that caressed his senses. He was aware of hovering in the borderland between sleeping and waking, where the slightest relaxation of attention would allow him to drift into sleep. A huge wooden cart with massive timber beams trundled across the threshold of his mind, while a female voice stated clearly: "All elephants are misfits in the world of fleas." An effort of will propelled him back toward consciousness, and he depressed the ninth button, on which his finger was already resting. He was immediately back in the corridor, running after the man in slave uniform. As he seized the shoulder of his tunic, the man stumbled and crashed sideways against the wall. The scene had the clarity of a dream, and was in such vivid detail that it seemed to be taking place in a kind of slow motion. The man was turning his head, and Niall was looking into the large eyes, and experiencing his sense of panic and desperation; it was so acute that Niall felt sorry for him. Then came the sensation of a violent blow, and the choking sense of suffocation. But this time, Niall saw the "blow" coming: the concentration of the will, the focusing of a beam of aggression, the deliberate assault on the control center of his nervous system. Then, as their minds came into contact, his own identity seemed to blend into that of his assailant, as if they had become the same person. For a few seconds, the man's whole life was spread out for Niall's inspection. What he saw shocked and repelled him. Once again, he experienced the unpleasant sensation, like a disagreeable smell, and this time was aware that it sprang from a certain ruthlessness and brutality. The sheer complexity of what he was seeing was bewildering, although its salient features were clear enough; it was a little like looking down on the Earth from outer space. He needed time to study and take it in.

But already the man was springing to his feet and reaching into his bosom; his hand was emerging with the knife as Niall touched the "off" control.

"Well?" Niall said: "He was a trained killer."

"Was Skorbo the intended victim, or was he chosen at random?"

Niall had to search his memory. It was like trying to remember a dream. "The intended victim."

"Where do they come from?"

"Somewhere. . . underground."

"Dira?"

"No, not Dira. Some. . . other place."

"Do you know where?"

Niall closed his eyes and tried to focus the memory, but it was no good.

"No. It all happened too quickly."

"That can be remedied, of course. What else did you find out?"

"Hatred. . . I could sense hatred. This man was a kind of trained butcher or executioner. And there was something else I didn't understand. . . He wasn't entirely human."

"In what sense?"

"I don't know. It was just something I felt."

There was a silence. Niall said: "It seems incredible. . . that there could be another underground city. Surely you'd know about it?"

The old man shook his head. "I am afraid our information-gathering system is not infallible."

"But a whole city. . ."

"There is a curious legend that dates back to the twentieth century, a legend of space travelers from a distant galaxy who landed on Earth when they were at the end of their resources. Solar radiation was deadly to them, so they built colonies underground, and created a complex civilization when mankind was still living in caves. But the hardships of living underground gradually caused their numbers to decrease. Many of those who were left began to suffer from a kind of insanity, so they turned into monsters."

"Monsters?"

"They ceased to behave rationally. Some of them began to eat human beings. The stories declare that these people were the origin of legends about vampires, ghouls, troglodytes, and other sinister creatures from underground."

"But is that true?"

The old man chuckled. "Torwald Steeg would have said that it was obvious nonsense. But he would also have acknowledged that it is impossible to know how much truth there is in a legend."

"Then how can we find out about this underground city?"

"At the moment, your main hope lies in the internalizer. Your minds were only in contact for a moment, yet you may have learned far more than you realize."

Niall reached for the control unit, then hesitated. "You say I should wait until tomorrow?"

"That is your decision. If you are tired, the results will be poor."

Niall's head ached and he felt exhausted; yet his curiosity was stronger than his fatigue. "I think I'll try just once more. . ."

He lay down, closed his eyes, and touched the "on" button. The headache dissolved away, and he experienced an overwhelming temptation to fall asleep. He resisted this and touched the second button. It was even more difficult to resist the waves of dreamy relaxation that tried to wash away his consciousness. Before this could happen, he touched the ninth button.

Once again he was in the rubble-strewn corridor with its smell of damp plaster.

But this time the experience was so vivid that it was hard to believe that it was unreal. As in a dream, the walls looked quite solid, and the floor under his feet was obviously hard.

His underlying tiredness seemed to sharpen his perceptions, with the effect of slow motion. Even as he was pursuing the man along the corridor, he could see the glue spider looking out of its hole in the ceiling, and this observation made him aware that his perceptions were not confined to his memory of the event. As if in a real life situation, he could direct his attention to anything he chose. As he reached out to grab the man's shoulder, he noticed a few links of the gold chain showing from under the slave garment.

Then the man stumbled and turned -- Niall felt that he now knew his face as well as that of his own father or mother; he also noticed the badly shaven chin and the oddly feral quality of his teeth. When the blow came, it seemed to be like a kick deliberately aimed at his solar plexus. He was interested to observe that the man was using a kind of emotional negative energy; it was as if he had looked at Niall with hatred, and the hatred had somehow turned into a physical force, like a clenched fist. And this, Niall now realized, was because it had been directed at his own emotional center.

As their minds came into contact he was again aware of his distaste, a desire to turn away his face, as if from an unpleasant smell. But this time he resisted the impulse, determined to try to understand as much as possible of the killer's life and background.

Again there was a vertiginous sensation of seeing too many things, so many that his mind had no chance to retain them.

It was at this point that the whole quality of the experience underwent a change.

So far, he had been aware that he was studying a kind of recording, a memory trace that had been fixed in time. Now, suddenly, he had the curious sensation of being in contact with a living mind. This was obviously absurd, since the man was dead. Yet the experience was unmistakable. The difference between studying a memory-recording and probing a living mind was as plain and distinct as the difference between touching the cold flesh of a corpse and the warm flesh of a living person. His mind recoiled in fear and alarm. In that moment he became aware that both he and Skorbo's killer were standing in a narrow stone chamber, in complete darkness. There was an impression of cold. A few feet in front of them, a man was seated in a stone chair that was not unlike the throne on which King Kazak had received visitors in Dira. In spite of the darkness, the man in the chair was completely visible, as if to some sense other than sight. He was dressed in a long, black garment like a monk's robe, and his face was concealed inside its cowl. Yet in spite of being able to see in the dark, Niall was unable to see the face inside the hood; only the whites of the eyes were dimly visible, and they seemed to stare with an unblinking intensity that was unnerving.

Dark shoes with curled tips peeped out from under the robe. The only other part of the man that was visible were the hands that rested on the arms of the chair. Niall observed that these seemed to be scaly, like the skin of a lizard or a snake, although the flesh was the color of normal human flesh. The fingers were connected together with a web of almost transparent flesh. In the moment Niall suddenly found himself in his presence, this man was apparently questioning Skorbo's killer, who was standing before him with bowed head, in an attitude of respect. But as Niall stared with astonishment at the man in the stone chair, Skorbo's killer seemed to sense Niall's presence; a moment later, the seated man also became aware of him. Niall had the impression that the eyes had narrowed, and as they turned on him, it cost him an effort not to take a step backwards; there was an almost physical force in the stare. His bodiless state seemed to amplify his sensitivity, so that he was abnormally conscious of the personality behind the eyes. Oddly enough, there was no sense of evil or malice; only of ruthless fanaticism that was akin to blindness. He sensed that this was a being who would regard anyone who opposed or disagreed with him as an enemy who deserved to be exterminated.

The man raised his right hand from the arm of the chair and pointed at Niall with a finger that seemed to have a claw instead of a nail; it might have been a gesture of admonishment. As he did so, Niall experienced an agonizing sensation in his chest. It felt as though some small crablike creature had leapt on to his chest and clung there, gripping with sharp little claws that seemed to extend in a circle, like those of certain bugs or lice.

The pain made him gasp; yet as his fingers tried to tear it away, he could see there was nothing there.

A moment later, he was back on the couch in the white tower, and the sun was streaming in through the window. His feeling of relief gave way to horror as he realized that the invisible entity was still tearing at his chest, as if intent on eating its way into his heart. The internalizer had been switched off, the room looked solid and normal. Yet he was still aware of the gaze of the narrow brown eyes, and of the intense pain in his chest.

As his hands clawed at the neck of his tunic, they snapped the fine gold chain that held the pendant round his neck; it flew across the room and landed on the floor. At that moment, the pain stopped, and he ceased to be aware of the brown eyes.

"What happened?"

Niall shook his head; once again, he felt drained and exhausted. But this time it was not the tiredness that follows a shock, but an aching sense of fatigue, as if he had just been subjected to some enormous strain that had brought him to the verge of physical breakdown.

He pointed at the pendant, which was lying against the wall. "That thing nearly killed me."

The old man picked it up. "That is impossible. It is merely a piece of metal."

Niall felt too exhausted to argue. He said: "It's some kind of transmitter. "

The old man shook his head. "My analysis indicates that it is an alloy of copper and zinc, with a trace of gold. It is quite solid, and therefore contains no transmitter."

"I don't give a damn what your analysis says." Niall was aware that his tiredness was causing his voice to choke with frustration. He forced himself to be calm, and allowed his head to sink back on the pillow. The peace machine immediately began to vibrate -- he realized this was an automatic response to his tension -- and he experienced an instant sense of relief. "Please switch that thing off." The vibrations ceased. "I don't want to go to sleep. I want to find out what happened."