"Revenge. The text says that this is a sigil dating from the thirteenth century, representing revenge. The lower part represents the wings of a bird of prey. The upper part represents the horns of der teufel, the devil. The bird of prey is winging toward its prey, carrying a terrible vengeance on its back."

As Niall stared at it, he felt a crawling sensation in the nerves of his scalp, as if someone had poured cold water over his head; it was like a premonition of danger. He examined the sigil intently, as if he could force it to give up its secret. "Does it say whether this was a famous symbol?"

"It doesn't, but the answer is almost certainly no. A symbol like this would be known only to students of hermeticism."

"Then how do you suppose Skorbo's killers knew about it?"

"That is something I cannot answer." He replaced the book on the shelf. "Perhaps they were students of magic."

As he followed Steeg back toward the elevator, Niall experienced a deep sense of frustration. It seemed absurd to be surrounded by so much knowledge, and yet to be baffled by a simple question.

"Why should anyone want to study magic?"

"Because it is far older than natural science."

"Yes, but. . . but surely it's just a kind of superstition?"

"That is what most people believed in the nineteenth and twentieth centuries. But in the twenty-first century, many anthropologists came to a different conclusion. They studied primitive tribes and concluded that some of them were able to perform certain feats of magic -- rainmaking, for example."

Niall shook his head. "Do you believe that?"

The old man smiled apologetically. "I do not believe or disbelieve. I am merely a machine. But Torwald Steeg was a rationalist, and he refused to believe it."

As they stepped into the elevator, Niall asked: "And how is magic supposed to work?"

"All primitive peoples say the same thing -- that magic is performed with the help of spirits."

"But spirits don't exist, do they?"

The old man smiled. "Torwald Steeg certainly did not think so."

The sensation of descending brought a return of the feeling of nausea; waves of heat seemed to be rising from his stomach. Niall pulled a folding seat out of the wall and sat down.

"Are you feeling ill?"

"Just tired." Niall closed his eyes and leaned his head back against the wall. "One of Skorbo's killers struck me with his will-force, like a spider."

"Although he was, in fact, a human being?"

Niall controlled his impatience. "Of course."

"I see." It was at times like this that it was obvious that the old man was a machine; he had no power to register astonishment. "In that case, I have a suggestion that might help."

The elevator rattled to a halt. As they stepped out, the old man politely held the door for a middle-aged woman in a tweed skirt; she gave them a tight smile as she stepped past them. In response to the silence around them, Niall automatically lowered his voice.

"Suggestion?"

The old man waited until they were outside before he spoke. "If your mind has been in contact with the mind of the killer, then he has left us a clue to his identity."

"How?"

"Every event is bound to leave a trace -- that is one of the basic principles of science. And it applies to mental as well as physical events."

Niall shook his head in bewilderment. "But how could you see a mental trace. . .

"It can be done -- with the aid of the peace machine." Again Niall's scalp tingled, but this time with pleasurable excitement. It was the sensation he experienced every time he approached the tower, the excitement a child feels when he hears the words "Once upon a time. . ."

His expression must have betrayed his feelings. The old man said: "Do not be too hopeful. The art of self-reflection is difficult and dangerous. But you will have to learn sooner or later. Come."

This time the old man led the way into the column. A few seconds later, they stepped into the hall of the peace machine.

This room was another of the Steegmaster's magical creations. Like the library, it was far too large to be accommodated in the tower. It was a broad gallery, about a hundred feet long, whose walls were covered with a rich brocade of blue and gold. At regular intervals there were pedestals with busts and statues. But the city Niall could see through its round-arched windows was not the spider city; to begin with, it was bathed in a sunlight so dazzling that waves of heat shimmered over its houses. The square outside contained a market, whose stalls were covered with bright-colored canopies, and the people who crowded between them were also dressed in bright garments; many of them carried swords. The city was surrounded by turreted walls, and beyond these there were green hills with terraces and vineyards.

But Niall was now so familiar with this panorama of fifteenth-century Florence that he paid it little attention. His eyes were fixed on the machine of blue-colored metal that stood in the center of the gallery. This consisted of a bed or couch above which was suspended a blue metal canopy whose lower face was covered with frosted glass. Even to look at it made Niall feel serene and relaxed. This was the peace machine, invented in the mid-twenty-first century by Oswald Chater and Min Takahashi, and capable of inducing a state of consciously controlled relaxation equivalent to dreamless sleep.

But as he was about to climb onto the couch, the old man raised his hand.

"Wait. Before you do that it is important for you to understand the principles of controlled self-reflection. Please sit down." He pointed to a bench that ran between the busts of Aristotle and Voltaire. "To enter the state without preparation could be highly dangerous.

"You know that the first thought-reading machine was invented in the early 2090s by a team at the University of Albuquerque, led by W. S. K. Sawyer. It was Sawyer who discovered that habit-memories have a molecular structure similar to that of DNA, and that an electric current can cause them to discharge. When you try to remember something without success, this is because you are too tired to cause the memory molecule to discharge.

"One day, an assistant of Sawyer's named Carl Meiklejohn was amplifying the memory circuits of an albino rat, and feeding them through to his own temporal cortex by means of electrodes implanted in his scalp. Suddenly, he discovered that the rat had formed a strong attachment to a pretty lab assistant named Annette Larsen. Now it so happened that Meiklejohn himself was in love with Annette, but had been too shy to show his feelings. So he naturally enjoyed studying the rat's feelings toward her. In fact, he enjoyed it so much that he began to make a habit of staying behind in the laboratory so he could play the memory circuits over and over again. One evening, when he was very tired, he fell into a half-sleep as he was playing the memory circuits. And in this state, he seemed to receive a strong impression that the girl was just as interested in him as he was in her. When he returned to his normal waking state, he was inclined to believe that he had been dreaming. But he had also noticed something else while he was half-asleep: that the girl had a circular patch of brown skin on her neck between her shoulder blades. The following day, he walked up behind her when she was peering down a microscope, and saw that she had a patch of brown skin precisely where he had seen it the night before.

This so impressed him that he asked the girl to go out to dinner with him. She accepted, and that night they became engaged.

"Now Meiklejohn thought a great deal about this experience. He asked the girl if she had ever allowed the rat to walk over her shoulders and the back of her neck; she said of course not. In fact, she had seldom taken it out of its cage. So how could the rat's memory contain the knowledge of the patch of brown skin? Now Meiklejohn reached an important conclusion. He recalled that the rat's memory had also told him that Annette was interested in him, and that this had proved to be true. So was it possible that the rat's memory contained far more than mere physical impressions of the girl: that because it was attached to her, it had somehow read her mind? And Meiklejohn, in turn, had read the rat's mind when he was half-asleep, and therefore in a state of deep relaxation.

"These conclusions were, of course, revolutionary. For it meant that a rat's memory is capable of recording impressions of remarkable complexity -- impressions too complex for the rat itself to understand. And that, moreover, Meiklejohn in his waking state was unable to grasp these complex impressions. He had to be totally relaxed and on the edge of sleep.

"Now Meiklejohn realized that he had made a discovery of tremendous importance, and that it would probably win him the Nobel Prize. So he decided to keep his discovery a secret until he had conducted some further experiments. And this proved to be a mistake. One morning, he was found wandering around the university building wearing nothing but his shirt, and in a state of psychotic anxiety. Attendants from a local mental hospital had to put him in a straitjacket. Under heavy sedation he eventually recovered, and told them what had happened. He had made recordings from the memory circuits of a stray dog. And the dog had belonged to an alcoholic who had treated it with extreme cruelty before he went insane. In a state of deep relaxation -- Meiklejohn had been using the peace machine -- he had played back the dog's memory circuits, and had been so shocked that he had an instant nervous breakdown. "The story has a happy ending. Meiklejohn married Annette Larsen, and made a complete recovery; he also received the Nobel Prize. And he went on to invent a device for recording and amplifying memories which he called the psychoscope -- a kind of telescope for looking into the mind. It became known to the general public as the internalizer. And the psychoscope led him to an even more important discovery: that he was able to study his own memories, and observe all kinds of complex impressions that he was not even aware of having received. For example, he discovered that Annette was pregnant at a time when neither of them had even thought of the possibility.

"Cheap forms of the internalizer became immensely popular toward the end of the twenty-first century -- people love to play with their own minds. But it caused so many nervous breakdowns, and so many cases of violent crime, that governments finally banned its sale, and made private possession of internalizers illegal."

Niall said: "But how could it tell me anything about Skorbo's killer? I only saw him alive for about half a minute."

"Your minds came into contact. That is enough. But before you try exploring these memory impressions, I would advise you to experiment with a few simple pictures."

Niall found it hard to conceal his excitement. What he had just heard seemed to open up almost unimaginable vistas of possibility. There was nothing to prevent him from exploring his own past like a picture gallery, from reliving the brightest moments of his childhood, or the excitement of his first visit to the underground city of Dira. His heart was beating almost painfully as he stood up and went to the peace machine.

"Where is this internalizer?"

"There is one already built into the peace machine."

Niall climbed onto the bed, and lay down under the frosted glass; the yielding velvet surface was as soft as eiderdown. A light came on behind the frosted glass, and there was a faint humming sound. The relaxation that instantly pervaded his body was so deep that he felt as though he was expelling the aches and fatigues of a lifetime. He had not even realized that he felt so tired, or that the encounter with Skorbo's killer had so drained his energies. Wave after wave of delight flowed from the soles of his feet up to his head, then seemed to retreat back again like the tide flowing back down a beach. In spite of his efforts to remain conscious, one of these waves picked him up and carried him into oblivion.

As soon as Niall opened his eyes, he remembered where he was. He sat up hastily.

"How long have I been asleep?"

"About two hours."

The thought filled him with guilt. "I must get back to the palace."

"Why? You are the ruler. You can do what you like."

This, of course, was true. Moreover, the Council meeting was over for the day. He allowed himself to relax again, adjusting the pillow under his head. Now he noticed the device that was lying beside him on the couch; it was made of half a dozen curved strips of metal in the shape of a cap. A wire ran from it to a socket in the side of the couch.

"Place that on your head and adjust it until it is comfortable." On the inside of each metal strip there were a number of felt pads; when Niall touched one of these with his fingertip he discovered that it was damp. He adjusted the cap on his head, with the front strip across his forehead, the rear one at the back of his skull. There was a faint electrical tingling where the pads touched his bare skin.

Behind the frosted glass screen, the light came on again; this time he was already relaxed, so it merely induced a warm glow of pleasure.

"Now, close your eyes and try to make your mind a blank."

Niall tried to imagine total darkness, and was surprised at his success. It was as if he was suspended in endless space. Then, with a suddenness that startled him, he heard his mother's voice.

"It has to be grated and pounded, then cooked for at least two hours. Otherwise it is a deadly poison."

He was so surprised that he opened his eyes to make sure that she was not in the room. Even with his eyes open he could hear her voice saying: "My grandmother used it to make a kind of wine."

The voice of his grandfather, Jomar, said: "She is right. It can also be ground into flour for making bread."

The old man asked: "What can you hear?"

"It's my mother talking to my grandfather."

And even as Niall answered, the conversation continued. Suddenly, Niall could recall exactly when it had taken place. He was about seven years old, and the family had only just moved into the burrow, the lair of the tiger beetle on the edge of the desert.

Before that, they had lived in a cave at the foot of the great inland plateau; but it had been hot, uncomfortable, and unsafe. By comparison, the burrow was cool and secure. When they first moved in, it had smelled of the acrid smoke of the burnt creosote bushes that had been used to drive out the tiger beetles. Now, as Niall listened to his mother and grandfather discussing how to cook the roots of the cassava plant, he could also smell the burnt creosote wood. There was another smell which he found more difficult to place; then it came back: the poultice made from the crushed root of the devil plant, which had been used to dress the wound in his grandfather's thigh -- a wound made by the mandibles of a dying tiger beetle.

As Niall lay there, he experienced many conflicting emotions and sensations. A part of him had become a seven-year-old boy, with all the feelings and thoughts of a seven-year-old. Yet he was also aware of his older self lying there on the couch of the peace machine, conscious of the presence of the child inside him. It seemed incredible that his memory had preserved this section of his childhood with such precision and exactitude, with every single word spoken by his mother and grandfather, and later by his cousin Hrolf, and Hrolf's mother Ingeld. And this recognition of the reality of his own past induced a feeling of elation, of sheer joy in being alive, together with a certainty that all the problems of human life are trivial, and that human beings only take them seriously because they are stupid and short-sighted. All these insights were so powerful that they seemed self-evident, as if he had known them all his life.

The old man's voice interrupted his thoughts. "Can you see where you are?"

"No."

"Very well. I want you to keep your eyes tightly closed, but imagine opening them." At first it was difficult to follow this instruction. When he tried to imagine opening his eyes, he felt his eyelids twitch, and caught a glimpse of the glass panel above him. Then he tried placing his hands over his eyes, so that it was impossible to open them, and envisaged lying on his bed of rushes in the burrow, with his mother only a few feet away. Quite suddenly, the cave was there, and he could see the face of his grandfather, illuminated by the single oil lamp. It seemed incredible that his father's father, who had been dead for more than three years, should be sitting there in all his living reality, talking to Niall's mother Siris, who sat with her back toward him. With a sudden total depth of conviction, Niall reflected that time is an illusion.

The old man said: "Have you succeeded?"

"Yes."

"Very well. Now I want you to try something rather more difficult. I want you to change this scene completely."

Niall said: "How?" The idea seemed absurd. He was there, in the cave, listening to his mother and grandfather, and waiting for his father and his uncle Thorg to return from a hunting trip.

"Imagine some other scene, and try to see it."

Niall tried to envisage the outside of the burrow, with its gray-looking shrubs and creosote bushes, and the treelike euphorbia cactus; but it made no difference. Then, suddenly, everything became dark. A moment later, his mother was saying: "It has to be grated and pounded, then cooked for at least two hours. Otherwise it is a deadly poison."

His grandfather's voice replied: "It can also be ground into flour for making bread.

The old man asked: "What is happening?"

"It's gone back to the beginning."

"Good. Now try again."

Niall tried concentrating. This made the voices fade; but when he stopped concentrating, they came back again. In some strange sense, his efforts seemed to be counterproductive.

The old man said: "Try imagining something that gave you great pleasure."

Niall tried to conjure up the first time he had seen Princess Merlew. She had been standing beside her father, King Kazak, in the throne room of the underground city, and her red-gold hair had been held in place by a circlet of gold. He could still remember the way his heart had lurched when she smiled at him, showing the white, even teeth that were unstained by the juice of berries. He could feel the softness of her skin as they clasped forearms in greeting. . .

Then, with a suddenness that startled him, he was holding her in his arms, and she was saying: "I've come to take you back with me." Her mouth was warm against his ear, and he could feel the curves of her body through the red spider silk of the dress. His own voice replied: "You know I can't do that." At that moment, Niall recalled that they were no longer in the underground city, but in the city of the bombardier beetles, and that he was waiting for an audience with the Master. And now Merlew was checking the door, to make sure the latch was secure, before she lay down on the couch, and drew him down beside her. His whole body was responding to the softness of her mouth as she pressed against him. His surge of desire was so powerful that he opened his eyes, embarrassed by the presence of the old man. Like a light being extinguished, the scene disappeared. But this time he was aware of what he had done to make it disappear. He had switched his attention elsewhere, like turning his head to look at something else.

The old man had also disappeared. Niall felt relieved, and at the same time amused with his own stupidity. The old man was a machine, yet his reflexes continued to treat him as a living reality. And all this training was designed to teach him to control his reflexes.

He readjusted the metal bands, pressing the contacts against his forehead, then closed his eyes and made his mind a blank. Once again he was surprised by the total darkness that supervened, as if he was suspended in empty space. This time he turned his thoughts to his cousin Dona, whom he had seen for the first time in Kazak's underground city. He was trying to conjure up the living quarters of the house where she lived with her mother Sefna. Instead, he found himself sitting beside her on a bench in the garden of the nursery in the spider city. The sunlight was warm, and there was a hissing sound as a fountain threw a spray of water into the air. A few feet away, his brother Veig was sitting on the lawn with Runa and Mara, telling them a story. And he and Dona were looking into one another's eyes, while cautiously allowing their fingers to touch. . .

As he now looked at her -- and she seemed as real as a living person -- he found himself wishing that Merlew had some of Dona's gentleness and kindness, and that Dona had a little of Merlew's jaunty vitality and seductiveness. Because the image of Merlew had so recently been present to his senses, he found it easy to conjure up her presence, as if he was still holding her in his arms. For a moment, Dona receded and gave way to Merlew. By a mental effort, he caused Merlew to recede, so that he was once again sitting beside Dona. It was as if he were in two places at once, and as if the two women were both trying to occupy his consciousness. Yet his consciousness was not a room in which Dona and Merlew jostled for space; it was a unified awareness in which both women were equally present. With a sudden flash of insight, he realized that this awareness was his awareness, and that it depended entirely upon his own power to sustain it. With a spontaneous and instantaneous mental gesture, he blended Merlew and Dona, so they ceased to be two persons. Merlew took on the gentleness of Dona, while Dona suddenly glowed with a new seductiveness.

This result astonished him. He had become so accustomed to the vagaries of the imagination, to his mind's inability to sustain a mental image for more than a few moments, that he found it hard to believe what had happened. It was true that this new Dona-Merlew was not as real as either of the two women; he was aware that if he reached out and tried to hold her hand, she would dissolve back into her constituents. Yet he could look at her, could study the amazing way that Merlew's pale skin blended into Dona's golden-brown complexion, and the way that Merlew's blue eyes and Dona's brown eyes united in an intermediate shade of green. Even their clothes had blended, and the new Dona-Merlew was wearing a nursemaid's blue tunic made of a clinging spider silk that emphasized the curves of her body. But what surprised Niall most of all was that the new girl, although less real than either Dona or Merlew, was undoubtedly a separate individual, a human being with her own unique reality. It seemed impossible to believe that she was merely a fantasy, a creation of his own mind.

The old man's voice said: "You may find it simpler to use this." When he opened his eyes, no one was there, but on the pillow, a few inches from his face, there was a small black box, about three inches square, whose upper face contained four rows of black numbered buttons. By now, Niall knew enough of electronics to guess that it was a control unit. And since the voice issued no further instructions, he cautiously pushed the first button. This was clearly the on/off switch. The curious sense of excitement and vitality disappeared immediately, and the world around him seemed to become solid and normal. It was a sensation not unlike waking up. When he pressed it again, he experienced a slight distortion of his senses that made him screw up his eyes; this passed, and he felt once again the electrical tingling that produced such an odd sense of expectancy and interest. The effect was not unlike that of the thought mirror with which the old man had presented him on his first visit to the tower; but the thought mirror amplified the powers of concentration, as if looking at the world through a magnifying glass, while this device seemed to induce a sense of relaxation and delight, as if the sun had emerged from behind a cloud.

This feeling disappeared as soon as he pressed the second button. This time the distortion of his senses made him feel sick and giddy; when it vanished, his body felt heavy and languorous, and he was overwhelmed by a dreamy sensation that made the world seem unreal; it was like being awake and asleep at the same time. He pressed the button again, but this only had the effect of increasing the dreamlike sensation until his senses blurred, and he felt as if he were hopelessly drunk. But as soon as he pressed the on/off switch, his senses cleared. It was an immense relief to be restored to everyday reality, and for the first time in his life, Niall realized that the sense of normality deserves to be regarded as a luxury.

The pleasure of exploration soon induced him to press the "on" switch. Then he pressed the button labeled "3." Nothing happened. He switched off and tried again. Still nothing happened. He knew that he merely had to speak aloud, and the voice of the Steegmaster would explain what was wrong. But he preferred to work it out for himself.

He stared at the device in his hand, and wrinkled his nose. The first button switched it on and off. Without that, the second button would not work. Perhaps the second button had to be pressed before the third would work? He tried it, touching the second button quickly and lightly -- he had already worked out that the intensity of the effect depended on how long he held it down -- and then pressed the third button. The darkness that supervened told him that his guess was correct. A moment later, he was startled by the sound of birdsong, and a noise of running water. At the same time, he could smell the indefinable yet distinct odor of wet grass and leaves. But since he was still in darkness, he had no idea where he was. Then, suddenly, he was in motion, and could hear the sound of wheels on the hard road, and of the feet of charioteers. He lay flat, and tried to imagine that he was opening his eyes. This time it worked immediately, and he found himself sitting between his mother and his brother in a cart pulled by four runners. They were passing through a stretch of woodland, and the branches overarched the road and formed a green tunnel. Between the branches overhead, the sky was a deep blue, but he could see storm clouds hanging over the distant hills; as they passed between two steep banks, he could reach out and touch the wet grass. They had just landed in the country of the spiders, and were being taken to the city of the white tower. On the sea voyage from North Khaybad, Niall had saved the life of a wolf spider who had been swept overboard; this is why they were being treated as guests instead of prisoners. And now, for the first time since his birth in the desert, Niall was looking at rain-soaked woodland and hearing the song of the thrush and the blackbird. It had been one of the most memorable sensations of his life, and now, as he experienced it again, he was bathed in a sense of delight and nostalgia.

Although it had been less than a year ago, it seemed to be in another lifetime, like a memory of childhood.

A moment later, this memory was suddenly replaced by another with which it seemed interconnected. This time he was marching along a moonlit road with a group of men who were dressed like slaves. In fact, they were young men from the city of the beetles, and they were setting out on a venture whose dangers were far greater than they realized: to try to gain access to the old fortress and its arsenal of weapons and explosives. Ulic, Milo, Yorg, Mostig, Crispin, Marcus, Hastur, Renfred, Kosmin, Cyprian were all drunk with the spirit of adventure; only Doggins, their leader, was aware of the danger. Within a few hours, three of them would be dead, including Cyprian, who was now marching next to Niall. . . But in the meantime, Niall breathed in the cold sweetness of the night air, and absorbed the enchantment of the silvery mist; some strange inner glow of optimism told him that tonight would change the whole direction of his life. . .

Now, at last, Niall felt he was beginning to understand some of the complexities of the internalizer. One memory had evoked another because they had some basic factor in common; and what they had in common was not simply that both experiences involved the countryside, but that both involved the same curious sense of delight and freedom.

He pressed the fourth button. Again there was darkness but a darkness in which he could hear the sighing of the wind, and smell the sharp, salty odor of the sea. Without even having to restore the sense of sight, he knew that he was standing on top of the high mountain pass that divided the desert from the coastal plain of North Khaybad, and that he was smelling the sea for the first time. His heart swelled with a tremendous exultation.

A moment later he was looking down on the green plain with its trees and bushes, and at the blue expanse of the sea that lay beyond. Then the vision blurred and darkened, and he was lying by a campfire, smelling the wood-smoke and the cold night air, and listening to sailors harmonizing the chorus of a sea shanty. He knew he was back in North Khaybad, on his way to recover the body of his father, and that their party was encamped in the midst of the same green plain he had seen from the high mountain pass.