"I don't know." He was feeling sick again, and had no desire to answer questions.

He turned to the overseer. "Please go to the headquarters of the Spider Lord and ask Dravig to come here." When the man looked alarmed, Niall turned to Simeon, whose face seemed oddly distorted, as if seen through water. "Would you mind going too? They'd pay more attention to you."

Before they were out of sight, Niall sat on the floor, his back propped against the wall. Waves of heat were rising to his forehead, and he could feel himself breaking out into perspiration. After a few moments, the nausea retreated again. He was breathing heavily, through his mouth, and his body felt drained of strength. But after resting for five minutes, a feeling of normality began to return. He opened his eyes, and looked at the dead man, whose face was turned upwards toward the ceiling. It was easy to see how he had succeeded in masquerading as a slave; he had a beaklike nose, large ears, and a receding chin -- only the abnormally pale face distinguished him from other slaves. But Niall recalled the strange glance of those dark eyes, and realized that he had been dealing with a man of intelligence. He had also been dealing with a man of formidable resolve; his instantaneous suicide proved that.

And he had, he now realized, been dealing with an alien, a man who was a native neither of this country nor of Dira. The proof was that the man had somehow learned the spiders' trick of striking direct at his will power. Yet there was an obvious difference.

When the pink glue spider had paralyzed him at the top of the stairs, it had somehow paralyzed his nervous system, so that he was fully conscious, yet unable to move a muscle. This man had used some direct, brutal psychic force, like a blow with a blunt instrument. It had left him feeling sick and weak, while the momentary paralysis of the spider had had no aftereffect. The difference was obviously that the spider intended only to stop him from moving; the man had intended to hurt him.

As he stared at the masklike face of the corpse, he experienced a strange sensation that sent cold waves through his scalp; for a moment, he was convinced that the man was still alive. It took him some moments to understand what had happened. His sense of bafflement had led him to make an attempt to probe the mind of the corpse. It was a purely automatic reflex, for he knew the man was dead. The result should have been totally negative, like stirring a dead body with his foot. Yet he had encountered an eerie sense of warmth and vitality. There was some sense in which the body was still alive and yet unconscious, like a plant or vegetable. Niall allowed his mind to become blank, and tried again. This time, he experienced a reflex of disgust which made him instantly withdraw, as if he had touched something unpleasant and slimy. There was something about the lingering life-field of the dead man that repelled him like an unpleasant smell. It was something as distinct as a smell, and therefore inexpressible in words. He had occasionally encountered it in the desert, in the minds of predators -- for example, in the nightmare creature called a saga insect, which had held a cricket in its claws and then crunched its way down its body as if eating a stick of celery. And he could still remember the revulsion he experienced on accidentally catching a glimpse into the soul of some demonic, batlike creature in the Delta; it had seemed to be entirely malevolent, as if consumed by the desire to kill.

The sound of footsteps brought him back to the present. It was Simeon, followed by Dravig. Niall started to rise to his feet, then thought better of it as the waves of nausea rose to his head. He sank down again, his back against the wall.

"Hello, Dravig. I'm sorry to bring you here."

"Are you hurt?" Niall was flattered by the genuine concern in the spider's query.

"No, I'll be all right."

Dravig looked at the corpse. "Who is this man?"

"One of Skorbo's assassins."

"You have done well. Where is the third?"

"I don't know. But now we know why they removed all the clothes of the dead man. He must have been dressed in a slave uniform, and they didn't want us to know he was hiding among slaves. I think it might be worth searching the slave quarter." "I will give the order. How did this man die?"

"He killed himself with that knife. Be careful." The spider had picked it up in his tarsal claw, and raised it toward his face. "It's poisoned."

"Yes. It is the venom of the green rock scorpion, perhaps the deadliest poison on earth." The spider's sense of smell was far more acute than that of a human being. "It is fatal even for spiders."

"Then you should warn the searchers to be careful. The other may be armed with one too."

The spider signified affirmation; the mental gesture was independent of words, like a nod. He asked: "Do you need help?"

"No, thank you. Simeon will help me."

"Then I must return to make my report." He drew himself up, as if standing to attention, and said formally: "In the name of the Spider Lord I thank you for hunting down this assassin." Niall understood enough of the spider mentality to know what he was trying to convey: that he accepted that the human beings of this city were in no way responsible for Skorbo's death.

Niall inclined his head. "Thank you."

When Dravig had gone, Simeon picked up the knife, and carefully replaced it in its sheath. "I'll get this analyzed. The poison must be deadly." He had been unable to hear Dravig's side of the conversation.

"It is the venom of the green rock scorpion."

"Great goddess!" Simeon almost dropped the knife. "If I'd known that I'd have picked it up with gloves." He took a large handkerchief from his pocket and carefully wrapped the sheath, tying the corners in a knot.

Niall pushed himself cautiously to his feet, and was relieved to find that he no longer felt dizzy; but the feeling of tiredness remained. Simeon looked at his face with concern.

"You're very pale. Did he hit you in the stomach?"

Niall shook his head. "He struck at me with his will-force, like a spider."

Simeon stared incredulously. "Are you sure of that?"

"Quite certain."

"He didn't touch you physically?"

"No."

Simeon absorbed this in silence. He looked down at the body, shaking his head.

"Then who the devil could he be?"

He dropped on his knees beside the body and searched the pockets. They yielded only a soiled handkerchief of coarse linen, and a wooden spoon and fork -- slaves carried their own eating utensils.

Niall said: "Look around his neck." There was, as he expected, a fine gold chain with a pendant.

Simeon removed it and held it out to Niall. "Do you want it?"

"No. I already have one."

But this was not the real reason he refused to take it. He felt a curious intuitive revulsion, a feeling that the pendant was somehow unclean.

Before he was halfway down the avenue, Niall realized it had been a mistake to walk. Every muscle in his body ached, and his feet felt as if they were made of lead. In spite of the sunlight, the cold air made him shiver. He brushed the snow from a low wall and sat down.

A few hundred yards away, in the center of the square, the white tower sparkled in the sunlight; its purity made even the surrounding snow look gray. As he stared at it, framed against the pale blue sky, Niall felt again the sensation he had experienced the first time he saw it: the curious spark of pure joy. He and his family had been prisoners of the spiders, and they had looked down on this city from a hilltop to the south. Some intuition had told him that the white tower represented freedom and hope. Now, as he looked at it, the surge of delight caused the exhaustion to vanish, and he realized that his mind had been increasing the fatigue by paying attention to it.

The tower stood in the midst of a square space of green lawn, now invisible under the snow. Even in the days of slavery, the spiders had allowed their human captives to trim the grass and keep it free from weeds. They had detested the tower, as a symbol of past human supremacy; they had even attempted to destroy it. Yet they had respected it as a mystery beyond their understanding.

In fact, the tower was virtually indestructible. What looked like semitranslucent white crystal was, in fact, an atomic force field, made to look solid by causing it to reflect the light; it rejected solid matter in exactly the same way that the pole of a magnet rejects the like-pole of another magnet. In the course of about a million years, the force field would drain away and the tower would collapse. In the meantime, it would continue to serve as a time capsule, a giant electronic brain whose memory cells stored the accumulated knowledge of the men who had once been the sole masters of the earth.

Now that he had regained his breath, Niall stood up and walked on toward the tower. The men and women who passed him hardly gave him a second glance; in his long cloak, with the fur-lined hood, he was indistinguishable from most of them. It was a relief not to have to return their salutations. During his early days as the ruler of this city, they had prostrated themselves on the ground and remained in that position until he had gone past. He had tried issuing a proclamation that he wanted to be ignored, but it had made no difference; the idea of ignoring their king shocked them profoundly. So Niall had issued a second proclamation, declaring that he preferred to be saluted with a bow. This time the citizens had obeyed him, but sometimes they bowed so deeply that they fell over, and Niall felt obliged to go and help them up. On the whole, he greatly preferred to be ignored.

The snow that covered the lawn around the tower was free from footprints.

Although there was no law forbidding citizens to walk on the grass, no one ever did so, even to take a shortcut; the tower seemed to inspire feelings approaching religious awe.

The white tower was thirty feet in diameter at its base, and about two hundred feet high. Yet as he looked up, it seemed to stretch as high as the clouds. This was an optical illusion, due to some quality in its milky surface, which seemed to shimmer like the air above a hot road; Niall had once compared it to liquid moonlight. As he approached within a few inches, he experienced the familiar tingling sensation throughout his body, the sensation a water diviner experiences as he stands above an underground stream. He felt as if he was being pulled forward by a magnet. The sensation became stronger as he made his way around to the north side of the tower, where he knew its vibrations were precisely attuned to those of his own body. There the pull became irresistible, and he moved forward. As his body encountered the surface, there was a sensation like walking into water. He experienced a momentary dizziness, a loss of orientation, as if he was on the point of fainting or falling asleep, and everything became dark. Then it grew light again and he stepped inside the tower.

Yet what faced him now was not the circular room he had anticipated, but a breathtaking panorama of snow-clad mountain peaks, ice-covered ridges, and misty blue valleys, stretching out in all directions for what seemed hundreds of miles. Clouds rested like feathery pillows in some of the glaciated valleys, but the clouds above his head looked as jagged and broken as the granite ridges and slopes far below. He was standing on a mountaintop on hard-packed snow, and the air was so clear that it seemed to sparkle.

Less than six feet in front of him there was a sheer drop into a valley that must have been at least a mile deep; to his right, a sloping ridge like a snow-covered rocky spine ran down to another peak far below.

Niall was startled, but not deceived. He knew that the scene spread out before him was an illusion. The first time he had entered the white tower, he had found himself standing on a sandy beach, facing a line of steep cliffs; that had also been a panoramic hologram, a film projected into three-dimensional space to produce an illusion of solid reality. Even the cold wind that now blew against his face was an illusion created by electronic technology; a stream of charged particles bombarded his nerve ends, creating an illusion of moving air. Yet everything looked so completely real that it was impossible to detect the deception.

He rubbed his feet on the hard snow; it felt exactly like the snow he had left behind outside. But as soon as he closed his eyes he was aware that he was standing on a smooth wooden floor. He took three steps forward, so he was standing on the edge of the sheer drop. Intellectually, he knew he was still standing on the hard floor. Yet when he tried to force himself to take an additional step into the void, his feet refused to obey him, and he experienced a rush of fear that almost took his breath away. He could see the worn granite face of the great slope opposite, with its snow-filled crevasses and razorlike edges, in the most precise detail. Yet as soon as he closed his eyes it all vanished -- even the cold wind -- and he knew that he was on a solid floor.

He walked two steps forward, then opened his eyes. He was suspended in midair, looking down at the striated rock face a mile below, and on the cloud-filled valley floor.

It was like floating on a magic carpet. He went on walking, now intellectually confident, while his emotions continued to sound frantic alarm bells and to flood his bloodstream with adrenaline. A few steps further, and they gradually became calm, leaving him suddenly relaxed and triumphant.

At that point the mountain landscape disappeared with the abruptness of a bursting bubble, and he found himself in the familiar room, with its curved white walls and luminous white ceiling. In its center there was a marble-colored column, more than three feet in diameter, stretching from floor to ceiling; it had the same texture as the outer walls of the tower, but seemed even more unstable, as if made of a kind of gray liquid smoke, which flowed as if it were alive. When Niall stepped forward into the surface, it admitted him, and he found himself surrounded by a white odorless fog. As if his body had suddenly become weightless, he was floating upward; it was such a pleasant sensation that he would have liked it to last for hours. But a few moments later he stopped with a slight jerk. A single step forward, and he was standing on a flat roof, with a pale blue sky overhead, and the panorama of the spider city stretched around him -- the view with which he had become so familiar from the roof of his palace.

This was not, in fact, a flat roof, but a room consisting of a force field in the shape of a glass dome. But a glass pane is visible because it has accumulated a layer of dust; the force field, being uncontaminated by dust, was virtually invisible.

This room was comfortably furnished; tubular metal furniture was covered with a black, leatherlike material that was warm and yielding to the touch; the thick black carpet was as soft as spring grass. The only unusual item was the tall black box that stood against the southern wall, with its sloping panel of opaque glass and row of control knobs. This was the Steegmaster, the creation of Torwald Steeg, which was responsible for this tower and almost everything in it.

Standing beside the Steegmaster, staring out over the square, stood a man in a gray suit. The tall figure was slim and upright; only the white hair betrayed that he was old.

He asked: "Did you recognize it?"

"It was the Himalayas, wasn't it?"

"Your geography is improving. You were standing on the summit of Mount Everest, looking south toward Nepal. The summit in the distance was Kanchenjunga."

It was a game they played every time Niall came to the white tower. Yesterday it had been the South Pole; two days before that, the crater of Mount Etna in full eruption.

Niall had guessed wrong both times.

He went and joined the old man by the window, and was surprised to see that the square was no longer empty. In the few minutes since he had entered the tower, a large contingent of men had formed ranks outside the headquarters of the Spider Lord; there must have been at least a hundred of them. As he watched they were joined by another squad who marched out of a side street. At an order from one of the black-clad commanders, all stood to attention. A moment later, the double doors of the headquarters building opened, and death spiders and wolf spiders began to emerge. They were marching in single file, and Mail recognized the spider at the head of the column as Dravig. They crossed the western side of the square and moved north toward the river; the slave quarter lay on its further bank. As the spiders continued to pour out of the building, Niall found it hard to believe that it could have held so many. By the time the doors closed, there must have been at least three hundred spiders on the march. The men, with two commanders at their head, marched behind them.

Niall asked his companion: "Do you know what is happening?"

"I assume this is connected with the death of the spider?"

"Do you know who killed him?"

The old man shook his head. "You overestimate the powers of the Steegmaster.

Its purpose is merely to gather and correlate information."

It was true that Niall had only the vaguest idea of the capacities or limitations of the Steegmaster; wishful thinking inclined him to regard it as an all-knowing intelligence.

"But you knew about the death of the spider?"

"Naturally, since it took place only a hundred yards away."

"But you've no idea who might have killed him?" "I would like to help you. But I lack the information to assess the probabilities."

"I thought the Steegmaster could read minds."

The old man said patiently: "Not minds. Thoughts. That is an entirely different matter. A thought-reading machine can decipher the information stored in the memory circuits of the brain, but it operates best when the person is asleep. It is almost impossible to read the thoughts of someone who is awake because the mental processes are too complex, and most of them operate on a subconscious level. The Steegmaster has no power to read feelings and intuitions, which operate on frequencies far beyond its range.

To work efficiently, the Steegmaster requires specific information."

Niall took from his pocket the pendant on its gold chain. He held it out on his palm, with the symbol uppermost. "How about this? Can you tell me anything about it?"

The old man studied it for a moment. "I would say that it is a magical sigil."

"Sigil?" Niall had never heard the word.

"A type of symbol used in magic or alchemy."

"But what does it mean?"

The old man smiled at him. "Let us see if we can find out." As he finished speaking, he vanished. And since he had been forewarned by the smile, Niall accepted the disappearance without surprise. Throughout their conversation, he had been aware that he was actually speaking to the computer that stood between them. Like the mountain range that had confronted him on entering the tower, the old man was a computer-created hologram; this was why Niall sometimes addressed him by the name of his creator, the twenty-third-century scientist Torwald Steeg. Niall was also aware of his purpose in disappearing, rather than leaving the room in the normal manner. Steeg's aim was to teach him a new set of reflexes and reactions; it was an attempt to make him trust his reason rather than his senses.

Now reason told him the old man would be found in the library. He stepped again into the column in the center of the room. As the mist surrounded him, he again experienced the sensation of weightlessness; his body seemed to be a feather drifting gently into a gulf. When the slight jerk told him that the descent had ceased, he stepped out of the column. Of all the rooms in the tower, the library was Niall's favorite; he loved to breathe its smell of dust, old parchment, and leather-bound books. To refer to it as an illusion would have struck him as a kind of blasphemy. The library, was, admittedly, a creation of the Steegmaster; but a creation of such complexity was in some way more real than mere physical reality. After all, what was reality but a force field of subatomic energies?

The library was a vast hexagonal room, about fifty yards wide, and so high that its domed ceiling was almost invisible. The walls were lined with bookshelves and with wrought-iron galleries that encircled the room; Niall had once counted them and discovered that there were precisely a hundred. Between these galleries ran black iron stairways whose steps, like the galleries themselves, had a fretwork design based on a motif of leaves and petals. On either side of the library, an old-fashioned cagelike elevator ran up to the topmost gallery.

These shelves, according to the gold plate above the door, contained copies of every book in the world, a total of 30,819,731 volumes. Every book had been photographed page by page and stored in the memory of the computer -- a project that had taken an army of scholars more than fifty years. The undertaking had been inspired by the notion of the twentieth-century writer H. G. Wells, who had advocated the creation of an encyclopedia encompassing the whole range of human knowledge. This library was even more ambitious than Wells's "world brain"; it contained, quite simply, every idea that man had ever committed to print.

The design of the room had been based upon a combination of the Reading Room of the British Museum, the Bibliotheque Nationale, and the Vatican Library. The center of the library was occupied by a large circular desk, staffed by librarians; from this, like spokes in a wheel, radiated blue leather-covered tables illuminated by reading lamps.

Niall had never discovered the identities of the people who sat at these tables and trod softly around the galleries; he liked to believe that they were real men and women of the twenty-third century, whose identities had been captured and preserved by the miraculous technology of Torwald Steeg.

The old man was standing at the central desk, talking to one of the librarians; now he turned and beckoned to Niall, pointing to the nearest elevator. Niall joined him as he was pulling aside the creaking concertina of a door, and followed him into the wood- paneled interior, whose rear wall bore the notice: "Maximum load three persons." The old man touched a button; nothing happened. He opened and closed the concertina door again; this time, the elevator began to rise slowly, with a soft, whining sound. Niall had no idea how all this was accomplished, and no desire to know; he preferred to bask in the illusion that he had been transported back into an earlier century.

They stepped out at the twenty-eighth level -- each level had its number cast in the ironwork of the front of the balcony. These galleries made Niall nervous, since the fretwork made it possible to see through the floor and the sides of the balcony, which were scarcely three feet high. He knew it was impossible to fall, yet would have felt more comfortable if the floor and wall had been solid.

As he followed Steeg along the gallery, Niall observed that many of the titles of the books were in Latin: Turba Philosophorum, Speculum Alchamiae, De Occulta Philosophia, Aureum Vellus; others were in Greek or Arabic. They halted before a shelf whose metal-engraved label read: Hermetica, KU to LO.

"What's hermetica?"

"Magical studies, named after the legendary founder of magic, Hermes Trismegistos -- Thrice Great Hermes." He reached up to the shelf and removed, with some effort, a large volume bound in black leather; Niall had time to read its title: Encyclopedia of Hermetic and Alchemical Sigils, before it was placed on one of the tables that stood in each angle of the hexagonal gallery. The book's edges were uncut, and the handmade paper was thick and unglazed.

The old man clearly knew what he was looking for; he quickly located a page toward the end of the volume. "I think this is what you are looking for."

The symbol on which he had placed his finger was unmistakably the same as the one on the pendant, in spite of some slight variations in shape.

Niall bent forward eagerly, then looked up, his face wrinkled in disappointment.

"What language is that?"

"German."

"And what does 'rache' mean?"