There were five of them here, but not all at the same time, since there are only four beds.

It was a carefully planned expedition." He pointed to garments on the bed. "Some of those slave tunics were manufactured for the journey. If you look at them closely, you'll see that they're made of a finer material than these" -- he pointed to the soiled slave tunics -- "which are the real thing. As soon as they could obtain real slave garments, they put their traveling clothes in a drawer. Someone might have noticed the difference. And they were anxious not to draw attention to themselves. That's why they left the windows uncleaned and why they haven't attempted to board up the front windows. Instead, they kept the inner door locked, in case someone climbed in through the broken window."

Dravig had been listening with deep attention. "Your powers of observation are remarkable. How did you come to develop them?"

"All hunters have to develop them or their catch would be poor. But in this case observation is less important than reason. You notice, for example, that these people were obsessively tidy -- these floorboards have been scrubbed until they're almost white. That reveals immediately that they were not slaves. And anyone who came into this room would realize it. So why did they not avoid that risk and leave the place as untidy as most slave dwellings? Because they have been trained to be tidy. To live in an untidy room would be worse than discovery."

Dravig said: "But they also had a woman who had nothing else to do. Slave women stay at home all day."

Niall shook his head. "You forget that she had already been captured by Skorbo.

Only men lived in this room the past few weeks, yet they have continued to keep it tidy."

He pointed to the soiled slave tunics. "These were probably left in the cupboard, waiting to be washed, on the morning they set out to assassinate Skorbo."

He was struck suddenly by another thought. "On that morning, there were only three of them left. Two were hanging up in Skorbo's larder. Is that why Skorbo was chosen as the victim -- because they knew that he was responsible for the disappearance of the other two? That would explain something that has been puzzling me. The tree that killed Skorbo must have been planted at least a year ago, probably more. And at that time, they had no reason to kill Skorbo -- he was simply the captain of the Death Lord's personal bodyguard."

"Then who was the chosen victim?"

"You."

"I?" It was the first time that Niall had seen Dravig taken aback.

Niall laughed. "I am only guessing. But who else? The Death Lord never leaves his headquarters. Next to him, you are the most distinguished spider in the city."

"But why should they want to kill me?"

"Why should they want to kill anyone? I believe these people are driven -- or rather, that their leader is driven by a consuming hatred of the spiders and their servants."

"But what could they hope to achieve?"

Niall realized, with wry amusement, that Dravig was beginning to credit him with some almost supernatural insight.

"We can only guess. If they hate your people, then presumably their ultimate desire is to destroy them, and to take their place as the rulers of the Earth." Here Niall was drawing upon his own memory of lifelong hatred of the spiders. But if Dravig guessed this, he was far too tactful to allow it to show. He only said mildly: "It is difficult to see how that could be accomplished."

Niall shrugged. "Whatever their plans, my guess is that Skorbo spoiled them. So they sent for reinforcements and decided to make Skorbo their first victim. And at that point, everything began to go wrong. Skorbo killed one of them and they had to conceal the body. They removed his clothes so we wouldn't guess he was pretending to be a slave. But by then, Skorbo had dragged himself out into the square and raised the alarm.

They couldn't escape through the fresh snow without leaving a trail. So they tried to blend with the squad of slaves outside. Even at that point they might still have escaped -- in fact, one of them did manage to slip away without being noticed. Fortunately, Simeon guessed what had happened, and we caught the other one at the hospital."

Dravig said: "And now they are all dead."

"Not all. There is still the girl."

"Ah yes. I still cannot understand what part the girl played in their plans."

Niall shook his head. "Neither can I. And she cannot tell us yet."

"We must guard her carefully."

"I shall." Niall looked around the room. "I think we should also leave a guard on this place, in case some of them should return."

"You think there may be more of them in the city?"

"Not now, perhaps. But when their master knows he has failed, I think he will try again." He was suddenly struck by a sense of the preposterousness of the situation. "But, in the name of the goddess, where are they coming from?"

"Our patrols have been instructed to search the area for fifty miles around the city.

There are no reports of intruders."

"I wasn't thinking about intruders. Where is their city?"

"There are no reports of large concentrations of human beings in the lands ruled by the Death Lord."

Dravig's impassivity, and the oddly impersonal manner in which he delivered information, produced in Niall a mixture of frustration and amusement. "How far do these lands extend?"

"I cannot give you precise figures. My people lack an interest in such matters. I would advise you to speak to the commander of the aerial survey force."

Niall was intrigued. The spiders never volunteered information about their political or military organization, so that even after six months of working with them, he knew little more than at the beginning.

"What is his name?"

"Your people call him Asmak."

"Where can he be found?"

"At the headquarters of the Death Lord. Shall I send for him?" "No. I'm going back now. There is no more to be learned here."

Dravig made ritual obeisance. "In that case I shall return to deliver my report."

Niall waited until he was sure Dravig was out of the building, then took from the drawer one of the stone figures, still wrapped in its cloth -- Dravig, he knew, would advise him against it. This he placed in the pocket of his tunic. He then replaced the clothing on top of the other figures, and closed the drawer. Finally, he took the flat wooden box containing the seaweed, wrapping it first in one of the slave garments to prevent the water from dripping.

The wolf spider was still standing on guard -- now, under observation from the charioteers, as rigid as a statue; a few scattered feathers drifting in the gutter were all that remained of the seagull.

Niall said: "I would like you to keep guard inside the house with the door closed. I will send another guard to relieve you shortly." It was not clear whether the spider understood; its two main eyes, and the four subsidiary eyes beneath, stared rigidly and unwaveringly into space. But by the time the chariot turned the corner at the end of the street, it had vanished into the house, and the front door was closed.

As they crossed the main square, Niall ordered the charioteers to halt beside the green lawn that surrounded the white tower. He then dismissed them, telling them to go and eat; his insight into their minds told him that they were ravenously hungry.

As soon as he approached the tower, he knew there was something wrong. It normally exerted upon him a peculiar feeling of attraction, like the pull of a magnet. Now this familiar sensation was absent, as if his body had been encased in some insulating substance. And in fact, when he reached out to touch the wall, there was no longer the sensation of plunging his hand into water; it was merely touching a solid surface.

This baffled him. He walked round to the north side, where the vibrations were usually stronger. It made no difference; the milky, almost translucent wall remained solid; it even looked solid, instead of appearing to shimmer, like some crystallized smoke.

Could it be the box he was carrying? He set this down on the marble platform that surrounded the base of the tower; but even as he did so, he knew it made no difference.

Next he removed from his pocket the stone figurine. As soon as his fingers touched it, he experienced a return of the sensation he had felt on first handling it, a mild vibration not unlike that of a living creature -- perhaps one of the carnivorous plants of the Great Delta.

And as soon as he placed it on the ground, he felt a return of the familiar tingling sensation induced by the force field of the tower. Even so, it seemed somehow duller, less powerful than usual. It was not until he placed the figurine on the grass that he experienced again that curious sense of vibrancy, as if the atoms of his own body were somehow resonating at the same rate as those of the tower.

He picked up the box, still wrapped in the damp slave garment; this made no difference. Then he stepped forward into the curious electrical embrace of the wall, which was like water tingling with living energy. A moment later, he walked out into the inner room of the tower, with its luminous curved walls.

It was the first time in many months that this had happened. He normally found himself in some strange and often frightening landscape. On one occasion it had been the yellow, sulfurous mists of Venus; on another, the boiling maelstrom of water at the foot of the Victoria Falls; once he had even found himself sharing a sunlit pond with other ani-malculae. But the Steegmaster, who had inaugurated this guessing game, clearly felt that now was no time for distractions.

Niall said aloud: "What's happening?"

As he spoke the words, the old man was standing in front of him, exactly as if he had been there all the time. He offered only the briefest nod of greeting. "The walls of the tower were designed to exclude potentially hostile entities."

"I do not understand."

"The creature you tried to bring into the tower was potentially destructive."

"But it wasn't a creature. It was a piece of stone."

The old man stared at him from under the bushy eyebrows. "Are you certain of that?"

"Quite certain. It was a kind of odd little statuette."

"Where did it come from?"

"A room in the slave quarter. It was the hideout of Skorbo's killers."

The old man shook his head. "I suspect you have been deceived. Describe the circumstances in which you found it."

Since this was precisely why he had come, Niall described the events of the past hour in some detail. The old man listened without expression -- Niall suspected that it was part of his present policy to accustom Niall to the fact that he was merely a machine - - then said: "I must see this artifact."

To Niall's astonishment, he walked into the wall and vanished. Niall stepped after him, and found himself standing in the sunlight -- it was always a slightly vertiginous sensation to walk through a solid wall and step into nothingness. The old man was already bending over the cloth-wrapped figurine on the grass. A few passers-by in the square apparently took him for someone like themselves, for no one paid any attention to him.

Niall found it impossible to resist asking: "Have you even been out here before?"

The old man shook his head. "There has never been any occasion for it."

He unwrapped the cloth from the figurine, and held it on the palm of his hand.

Niall said: "Well?"

"I admit that I cannot understand why it has produced this anomalous reaction. It is clearly a piece of silicate mineral related to nephrite."

He turned and once again vanished through the wall of the tower. Niall followed him in. The old man was still studying the figurine -- Niall observed that it was the one with closed eyelids -- in the palm of his hand. He shook his head. "I must confess that this problem is beyond the capacity of my information circuits."

Niall could not repress an ironic smile. "You mean it contradicts Steeg's conception of the universe?"

"Precisely."

"Doesn't that suggest that your information circuits need to be extended?"

"That inference seems reasonable." Niall reflected that the advantage of a machine is that it is not ashamed to admit that it might have been wrong.

"What do you propose to do?" "First of all to neutralize it."

He placed it on the floor, then stepped back. What happened next made Niall jump. A beam of intense blue light stabbed down obliquely from above, illuminating the figurine. There was no obvious source of light; it appeared to emanate from the plain white surface of the ceiling. In its glow, the figurine appeared to be faintly luminous. The air around them became suddenly chilly.

Niall asked: "What's that?"

"A cold beam."

"I thought they were green."

"They normally are. But this one induces a temperature of absolute zero, reducing all the molecules to immobility. If there is any vestige of life, it will be placed in suspended animation."

"Wouldn't that destroy it?"

"Not if the freezing process occurs rapidly enough. In the great ice ages, fish were sometimes frozen instantaneously in rivers, and were able to swim away when the ice melted."

The temperature had plunged swiftly; Niall's breath now turned to vapor as he exhaled. But as he shivered and pulled his cloak around his neck, the blue beam vanished, and the room seemed to become instantly warmer. Water vapor immediately froze around the figurine, turning it white. Niall winced as the old man bent and picked it up, aware that his own flesh would have been seared as if by a white hot iron. After contemplating it steadily for several seconds -- Niall was aware that he was performing some kind of analysis -- the old man once again stepped into the wall. A few moments later he reappeared, but this time without the figurine. In answer to Niall's look of interrogation he said: "The cold had neutralized its force. But caution suggests that it would be better left outside."

"Have you any idea of the nature of the force?"

"None, except that it is biological."

"What makes you so sure?"

"Because it was neutralized by the cold."

"But you admit that Steeg didn't understand it?"

"I admit that he made no allowance for it in creating my information circuits."

"Doesn't that suggest that he may have been mistaken about the existence of magic?"

"Magic signifies supernatural interference in natural processes. Steeg regarded that as a primitive superstition."

Niall said patiently: "Look. A group of murderers came to this city carrying pendants inscribed with magical symbols of revenge. They also brought stone figures that appear to be alive. Surely Steeg himself would have agreed that this was something beyond his understanding?"

"Steeg knew that the universe is full of things beyond his comprehension. But he would have denied that these things can contradict the basic laws of logic and reason."

"Perhaps they don't. Perhaps they simply obey a different kind of logic."

"What are you suggesting?"

"Well, you have hundreds of books on magic, don't you? Some of them must contain clues about what's going on. Couldn't you find out?" "You are asking me to make a comprehensive search of more than three thousand volumes."

"Could it be done?"

"Of course. But it would take a long time."

Niall's heart sank. "How long?"