CALIBAN walked the night, burning with curiosity. He was a great distance from his starting point, in a quiet residential area, the walkways all but completely deserted at this hour. The homes were large and widely scattered. Great lawns, some of them getting a bit dry, scruffy, and thin-looking, separated the houses. In this part of town, it seemed there was little ground traffic to speak of. Judging from the absence of a road wide enough for large vehicles, travel to and fro was by aircar or by foot.

But a dying lawn was no less wondrous than a live one to Caliban. All the world was new to him, everything that he saw was a fresh and vibrant wonder. He saw the bright pinpoints of light in the sky and wondered what they were. He noticed a few bits of litter blown against a fence and wondered how such a strange combination of objects had come to be there. His datastore was mute on both of those subjects, and many others besides, but on the whole it was a splendid guide, telling him any number of things about the city through which he walked. He wandered everywhere, eagerly looking about at everything, marveling at all things. And if stars and litter were not explained, many other things were. More often than not, he could look at a thing, and wonder about it, and find that the datastore could identify it and explain it for him.

He was content for some time to wander the city, passively absorbing whatever the datastore saw fit to tell him about what he saw. Then Caliban had an idea. If the map and the datastore could work to tell him about what was before him, could they not also guide his steps? Perhaps he could examine the datastore ' s map, select an interesting destination, and travel to it.

He stopped in his tracks and tried the experiment. The outside world seemed to fade from his sight. Suddenly he was looking down on a map-schematic of the area he was in, done in bold primary colors and carefully designed symbols.

He tried to push outward from that point and was greatly pleased to discover that the simple act of wishing it to be so allowed him to visualize the entire city map, or focus in on any portion of it. Nor, he found, did his virtual viewpoint have to stayabove the map. He could move down to ground level and see the buildings and hill tower over him. He could visualize the map data from any angle or position.

A few moments of experimentation confirmed it: He could manipulate his viewpoint to any spot in or over the map, look at the lay of the land from a bird's-eye view, or from ground level at any position, with the buildings and streets presented in the proper shapes and sizes. His vision swept along great swatches of the city, across the parks, the buildings, the great roads. It was as if he were traveling through those places in his mind. The sensation was exhilarating, almost one of flight.

There were datatags on the map, offering information on the buildings-their names and addresses, and in many cases the names of whatever businesses went on there.

Suddenly he got a splendid idea. He could use the datatag information to learn more about himself. He manipulated his viewpoint within the map and brought it back to his present position. Then he proceeded to retrace his steps back to the building he had started out from. He could read the datatags connected to the building and learn what sort of place it was, see what other information the map held concerning it. Certainly he could find clues to his own identity, his place in the world. Eager to find out more about himself, he moved his viewpoint rapidly across the map, back the way he had come.

The map imagery rushed past him at a breakneck pace, twisting and turning violently, reversing his movements at tremendous speed. At last the images came back to his starting place. He made a strange discovery: The image of the building was incomplete. Nearly every other building was shown in great detail, with doors and windows and basic elements of the architecture clearly shown. But the map showed this building as nothing but a featureless grey rectangular solid, a low, long shape on the land.

Confused, Caliban accessed the datatag system.

And discovered that the map had no information whatsoever about the building inside which he had awakened.

Stunned, surprised, Caliban shut down the map display system. The bright colors and symbols of the map faded from his vision, and he found himself once again standing in the darkness, alone on an empty pathway in a quiet residential district.

Whywas there no information about that building? Perhaps he should go back there, examine the place firsthand. He of course had a perfect, detailed memory of what he had seen there, and no doubt he could work his way back through those memories for information. But he had not been looking for anything when he awakened, had not even been fully aware that he should have known more than he did. If he went back, he would learn more.

He turned around, was about to head back the way he had come, toward the lab. But then he stopped. Wait a moment. There was another factor. One he had not considered yet. He recalled that first moment of awakening, the sight of the woman unconscious at his feet, the blood pooling about her head. The cross-index system of his datastore flitted through a whole series of things even as he thought about that moment.

And it settled at a quotation from the Legal Code that leaving the scene of a crime before being interviewed by the police was itself a crime. His mind flittered through all the datastore had to say about the Legal Code, the concept of crime, and the idea of punishment and rehabilitation. All of it seemed to relate to humans, but it was not a great leap of reasoning to assume that committing a criminal act could mean trouble for a robot as well.

No, he could not go back there.

Wait a moment. Were there other blanks on the map? Other places where detail was limited in some way? Perhaps other places with limited information on the datastore would have something in common with the building he had left. Perhaps examining one ofthem would offer some clue; perhaps some thought or image would stimulate the datastore to offer some sort of information that could tell him about himself.

Caliban looked about the area and decided it would be best to get off the pathway while he was examining the map. He stepped off the path and walked a short way, until he found a slight depression in the rolling landscape. He sat down in it, reasonably sure he could not be seen from the path.

He returned his attention to the datastore map. At first, his mind cast back and forth across the map in random, swooping passes, trying to cover as much ground as quickly as possible while still keeping track of any building or place that seemed suspiciously blank. Then he resolved to quarter the whole city and go block by block, in an orderly manner. Perhaps there was something he could learn from the pattern of blanked places, something he could discern only when he had located them all.

The map of the city had definite edges to it, precise boundaries beyond which was nothingness. Caliban's knowledge of the world, the universe, stopped at those borders. For a moment, Caliban toyed with the idea of venturing to the closest of those boundaries, just to see what it was like. He imagined himself standing on the edge of the world, looking down into nothingness. The idea was exciting and disturbing.

But no. It would not do to get sidetracked. First he must get answers about himself and about what had happened at the building where he had awakened. After those two mysteries were resolved, he could take the time to indulge his idle curiosity.

He set to work at the southern edge of the map and began to work across it methodically, examining a strip from east to west, then moving northward to examine the next strip, west to east.

And then he found it. Not far from the southern edge of the map was a great void, an emptiness a thousand times, ten thousand times larger than the blank, unmarked building in which he had awakened. But this was no area without detailed markings. This was emptiness, the absence of all things. No land, no water, no buildings, no roads. There was nothing there at all.

He wondered if the map was reporting literal truth. What could such a void look like in real life? What would cause it? His curiosity, his eagerness to see this place, was all but uncontrollable. But he held firm to his plan. He must examine the whole city, absorb the whole of the datastore map into his active memory. There could be other voids as well, equally significant. He held to his search pattern, moving south to north, shuttling east to west, west to east.

It took the better part of an hour, but at last Caliban had worked his way across the whole of the map of Hades. Yes, there were other voids, but none of them were even a fraction as large as the first he had found. Yes, there were other unmarked, unlabeled buildings, but he could not see any obvious pattern, no relation to the features on the rest of the map, that told him anything meaningful, or anything at all.

There was nothing left for it but to go and look. Now there was no reason to resist the temptation to see what the great void looked like. Caliban stood up and walked back to the field, using his infrared vision to move easily through the darkness.

The site of the void was a good distance across the city, and the first hints of dawn were lighting the east as he traveled through the semi-arid, half-populated expanses of Hades, imagining what a great emptiness would look like.

But what he saw when he got there was no blank on the map. As the dawn broke full over the horizon, Caliban stood at the edge of where the map said there was only emptiness.

What Caliban saw was a lively oasis in the midst of the fading city. He stood at the edge of a broad and verdant park, dotted stands of trees, great lawns, spraying fountains.

Small pavilions dotted the landscape and seemed to give access to underground facilities, judging by the people going in and out. Caliban walked along the low stone wall that formed the perimeter of the park, until he came to the entrance.

Settlertown,a sign said. Caliban stared at it in confusion. Another mystery. He had no idea what Settlers were, or why they should have their own town. He called to the datastore, but it had no information on any such term.

For some reason, all information regarding both his origin point and this place had been deleted from his datastore.

But why would anyone do that?

DARKNESS had passed, and dawn had come over the horizon, and the morning was well begun. Alvar Kresh paced the room, listening to the routine words of the routine interrogation of yet another routine coworker, one Jomaine Terach. Terach wasn't normally up and at the lab by this hour, but he lived quite near the lab and all the commotion had wakened him. He had wandered over to see what was going on-or so he claimed. Police officers throughout history had been a little slow to believe witnesses who explained trifles such as coming to work with such elaboration-and Kresh was tempted to uphold that tradition in the present instance. It would be wise to treat everyone as a suspect just at the moment.

Kresh let Donald do most of the work. This night had been a long, hard journey through the darkness to the day. Crime scenes could be grueling.

They had taken over the duty office for the purpose of doing the intake interrogations, taking each worker as he or she arrived. The duty office was designed to accommodate an overnight stay, in case an experiment ran all night. The office featured a large and rather comfortable-looking bed, much better than the miserable cot in the duty room at Sheriff's HQ. After a sleepless night, it looked more than slightly inviting.

"Tonya Welton claims that Fredda Leving was-is-working; for her. Is that true?" Donald asked.

"Absolutely not," Jomaine Terach said, yawning mightily. "Fredda Leving has never worked for anyone but herself in her life, and she isn't likely to start in by oiling up to the high and mighty Queen of the Settlers." He yawned again. "My God, it's early. Have you been at it since the attack?"

"Yes, sir. We have been here working straight through the night," Donald said.

"So she and Tonya Welton don't get along," Kresh said, brushing aside Terach's and Donald's pleasantries. He sat back down at the table, next to Donald and opposite Terach. He drummed his fingers on the desktop, trying to keep his exhausted mind from wandering. Maybe he should have gone home instead of staying here all night.

Now, where was he? Damn it, his mind was wandering. He was getting fuzzy. He wasn't going to learn much of anything if he was too exhausted to think. "So they didn't like each other," he said again, trying to cover up his overlong pause. "Were they at least polite around each other?"

"No, sir, not in the least," Jomaine said. "Not anymore. They used to be much closer, real friends, I thought. Now there isn't much left but the professional relationship."

Thatwas an interesting tidbit. Tonya Welton and Fredda Leving, each with a real reputation for being a hard-edged infighter. He could easily imagine them coming to a parting of the ways. It was far harder to imagine them becoming friends in the first place.

But being personally involved with the victim made it just that much more peculiar that Welton would barge into the investigation. She must have known that Kresh would quickly learn about the friction between herself and the victim. It was very early in the going, but right now, she was the one with the best motive for the attack. Why draw attention to herself?

Alvar Kresh leaned back in his chair and looked across the desk at the man he was interviewing. Jomaine Terach was a tall, thin man, sandy-haired, pale, with a long, thin face and a sharp-pointed nose. There was something a bit overrefined, overformal, about his manner of speech.

Kresh repressed a yawn. It hardly seemed worth staying up all night just to listen to the likes of Terach.

Alvar rubbed his eyes and brought his mind back to where he was in the questioning." I find it hard to imagine the two of them as friends. Settlers hate robots, and Leving was one of the leading proponents of more and better robots. I can't see how much they would have in common," Kresh said.

"I think perhaps that was part of what made the friendship work-at least for a while. They enjoyed debating each other. But then things fell apart between them. Maybe it just got a little too intense," Terach suggested.

"But if she wasn't Tonya Welton's employee, Master Terach, and they were no longer friends," Donald 111 said, "might one ask what their relationship was?"

Terach glared at Donald. It clearly annoyed him to be questioned by a robot. But he was smart enough not to protest out loud.

Kresh watched Terach with a detached, professional interest. He often ordered Donald to take an active part in the questioning. It was a variation on the ancient good-cop, bad-cop routine. Donald unsettled the interrogation subjects, and then the subjects answered Kresh, looking to him for support and understanding, unwisely trusting him over Donald.

"They were collaborators, I suppose." Terach turned toward Kresh. "There's a lot I can't say about the work at the lab," he apologized.

"I've heard that more than once," Kresh growled. "Every employee I've talked to has told me that. Those seem to be the only words most of your people know."

"I'm sorry about that."

"Don't be. We'll be back once I've gotten the Governor to grant me some clearances."

That prospect didn't seem to please the rather reedy-looking Jomaine Terach. "Well, perhaps you needn't bother, once the public announcement is made."

"And I've heardthat, too, and I know bloody damn well you're about to tell me you can't say anything more," Kresh said. "So let's talk about something else. Tell me why Fredda Leving would be in Gubber Anshaw's lab in the middle of the night."

Terach seemed genuinely astonished. "Oh, my heavens, I wouldn't attach any great importance tothat," he said. "We're in and out of each other's labs all the time. The work is of a highly-ah-collaborative nature, and I expect that she was simply working on some subcomponent that happened to be in his lab."

"Infernals tend to be rather territorial people," Kresh suggested. "We like to have our own space."

Terach shrugged. "That may be so, but that doesn't meaneveryone is compulsive about it," he said, a bit pointedly.

"Mmmph," Kresh grunted, not altogether convinced, and ignoring the gibe that was clearly intended to distract him. "Well, then, maybe you can tell me where the devil Gubber Anshawis. He hasn't shown up this morning and we have not been able to reach him at home. We assume he's there, but his robots flatly refuse to confirm that, or to pass on any messages."

"I'm not surprised," Jomaine said. "Gubber likes to work at home, in complete privacy. He's taken to doing it more and more recently. Sometimes we kid him that if you police threw an arrest perimeter around his house, he wouldn't even notice."

Kresh grunted noncommittally. Privacy, and the sanctity of the home, were indeed highly valued commodities on Inferno. Indeed, it was illegal to arrest a person in his or her home. The law was very precise on that point, and on the procedures that could and could not be followed. The police and their robots could wait outside until hell froze over, they could search the premises once an arrest was made, but they could not enter the home to effect the arrest.

It had happened more than once that a suspect had refused to come out for a long period of time. Precedents and rules of procedure had long ago been established in such cases, setting out what could and could not be done. The police could cut off all communications links to the surrounded house, but not food, or water, or power. Sometimes the prohibition against home arrests actually worked to police advantage: If kept up long enough, the police-robot vigil outside a suspect's home amounted to house arrest without all the bother and expense of a trial.

"Well, it might come to an arrest perimeter if we don't hear from him soon," Kresh said warningly. "You might get that information to him."

Jomaine cocked a surprised eyebrow at Kresh. "Have a little patience, Sheriff. Gubber rarely comes in much before midday on the days he does come in," he said. "He spends his mornings at his home, working on other research projects. Most days-but not all of them-he comes in here and works on Leving Lab projects about midday and through the evening. But as I said, he doesn't always come in. He's not held to any sort of schedule."

Jomaine thought for a moment. "Come to think of it, I don't recall seeing him when I came through here last night. I doubt he was here. My guess is he's been at home, working, the entire time, quite unaware that anything has happened. And yes, his robots have strict orders to prevent his being disturbed. But that is routine with him. I wouldn't suggest that you read anything into his absence, or waste any time thinkinghe had something to do with the attack on Fredda."

Alvar Kresh frowned. "Why not? It was his lab she was attacked in. At this point we have no suspects, no motive, no real information at all. I don't know Gubber Anshaw or anything about him. I see no reason to eliminate anyone at this point, especially someone who would seem to have the opportunity to commit the crime. Coworkershave been known to have motives for murder."

"Well, there's your argument against suspecting him right there," Jomaine said, a bit overeagerly. "Gubber Anshaw had no motive for attacking Fredda, and every reason for wishing her well. I suppose, yes, hemight have had the means and the opportunity to assault her-but Sheriff Kresh, you have the means and the opportunity to pull your blaster from your holster right now and vaporize my head. That doesn't mean youwill do it. You have no motives for killing me-and a lot of motives fornot hurting me. You ' d lose your job and get thrown in jail, at the very least. But it goes past that. Fredda was a great help to Gubber. He would most definitely not want to lose that."

"You are suggesting that Gubber Anshaw would have a great deal to lose if something happened to Fredda Leving?" Donald asked.

Jomaine Terach looked cautiously at Donald, and then at Kresh. "Once again, that gets us into classified areas. But yes, I think that would be safe to say. Gubber had made some remarkable advances, advances that required the rejection of some very tried and true technology in favor of something newer and better and more flexible. However, he didn't get far in promoting his discoveries. Robotics is in many ways a very conservative field. Leving Labs was the only place that was willing to use his work."

"I suppose we're talking about gravitonic brains here," Kresh said.

Terach breathed in sharply, clearly surprised and unsettled. "How did you-"

"There was a stack of them in neatly labeled boxes in Anshaw ' s lab," Kresh said, more than a bit sardonically. "I think perhaps you need to work a little on security procedures down at the lab."

"Apparently so," Terach said, clearly nonplussed.

"So what the devil are gravitonic brains? Some sort of replacement for the positronic brain?"

Donald turned his head toward Kresh. "Sir! That would be quite impossible. The positronic brain is the basis, the core, of all robotics. The Three Laws are intrinsic to it, built into its very structure, burned into its fundamental pathways."

"Take it easy, Donald," Kresh said. "That doesn't mean that the Three Laws couldn't be built into another form of brain. Right, Terach?"

Terach blinked and nodded, still a bit distracted. "Of course, of course. I really cannot say anything specific about gravitonic brains, but I suppose it can't do any harm to speak in broad generalities. Gubber Anshaw is really just at the beginning of his research on gravitonics, but in my opinion he' s already made tremendous breakthroughs. It's time someone did."

"How do you mean?"

"I mean that we have rung out the changes on positronics. Certainly today's positronic brain is far superior to the original units. It has been greatly advanced and improved. There have been many refinements in it. But the positronic brain's basic design hasn't changed in thousands of years. It would be as. if we were still using chemical rockets for spacecraft, instead of hyperdrive. The positronic brain is an incredibly conservative design that puts tremendous and needless limits on what robots can do. Because the Three Laws are embedded in its design, the positronic brain is seen as the only possible design for use in robots. That is an article of belief, of faith, even among robotics researchers. But gravitonics could change all that.

"Gravitonic brains currently have one or two minor drawbacks, but they are at the beginning of their development. They promise tremendous advantages over positronics, in terms of flexibility and capacity."

"Well, you certainly sound like a true believer yourself," Kresh said dryly.There is none so faithful as the converted, he thought. "Very well, Terach. I may well wish to talk with you later, but that will do it for now. You may go."

Jomaine nodded and stood up. He hesitated before heading for the door. " Ah, one question," he said. "What is the prognosis for Fredda Leving?"

Kresh's face hardened. "She's still unconscious," he said, "but they expect her to awaken sometime in the next day or so, and go on to a rapid and complete recovery. They are using the most advanced regeneration techniques to stimulate recovery. I understand her head injury should be completely healed within two days."

Jomaine Terach smiled and nodded. "That's excellent news," he said. "The staff here will be delighted to hear it-ah, that is, if I'm allowed to tell them."

Kresh waved his hand in negligent dismissal. "Go right ahead, Terach. It's public knowledge-and she's under heavy guard."

Terach pasted on a patently false smile, nodded nervously, and left the room.

Kresh watched him go. "What's your reading, Donald?" he asked, without looking over at the robot. No one talked about it much, but advanced police robots were specially engineered to detect the body' s involuntary responses to questions. In effect, Donald was a highly sophisticated lie detector.

"I should remind you that Jomaine Terach quite possibly knows about my capabilities as a truth-sensor. I have never met him before, but a records-check confirms that he was on staff here during my construction. That does add a variable. However, suffice to say that he was highly agitated, sir. Far more so than any of the others, and, in my opinion, more so than would be accounted for solely by surprise and concern over the attack on Lady Leving. Voice stress and other indicators confirm that he was concealing something."

That didn't surprise Alvar. All witnesses concealed things. "Was he lying?" he asked. "Lying directly?"

"No, sir. But he was most concerned to learn we knew about the gravitonic brains. I found this confusing, as he went to some length to discuss them. I formed the impression that he was intent on steering the interrogation away from some other point."

"You caught that, too, I see. The damnable thing is that I can't imagine what point he was trying to lead us away from. My hunch is he thinks we know more than we do."

"That is my opinion as well."

Alvar Kresh drummed his fingers on the table and stared at the door Jomaine Terach had used to leave the room.

There was more going on here than the attack on Leving. Something else was up. Something that involved the Governor, and Leving, and Welton, and the Settler-Spacer relationship on Inferno,

Indeed, the attack was already beginning to recede in importance in his mind. That was merely the loose thread he was tugging on. He knew that if he left it alone, the rest of it would never be revealed. Pull it too hard, and it would snap, break its connections to the rest of the mystery. But play the investigation of the attack carefully, tug the thread gently, and maybe he could use it to unravel the whole tangled problem.

Alvar Kresh was determined to find out all he could.

Because somethingbig was going on.

JOMAINE Terach left the interview room. His personal robot, Bertran, was waiting outside in the hall and dutifully followed him as Jomaine hurried back to his own laboratory.

Sheriff Kresh had made Bertran wait outside the room during the interrogation.It was just a little harassment, Jomaine told himself,another way for Kresh to get and keep me unnerved. And yes, he admitted to himself,it had worked. Spacers in general, and Infernals particularly, did not like to be without their robots.

Only after he was in his own lab, only after Bertran had followed him in and shut the door safely behind him, did Jomaine allow himself to succumb to the fears he was feeling. He crossed the room hurriedly. He dropped back into his favorite old armchair and breathed a sigh of relief.

"Sir, are you all right?" Bertran asked. "I fear the bad news about Lady Leving and the police interview have greatly distressed you."

Jomaine Terach nodded tiredly. "That they have, Bertran. That they have. But I'll be fine in just a moment. I just need to think for a bit. Why don't you bring me some water and then retire to your niche for a while?"

"Very good, sir." The robot stepped to the lab sink, filled a glass, and brought it back. Jomaine watched as Bertran went over to his wall niche and dropped back into standby mode.

That was the way it was supposed to be. A robot did what you told it to do and then got out of the way. That was how it had been for thousands of years. Did they really dare try and change that? Did Fredda Leving truly think she could overturn everything that completely?

And did she truly have to make a deal with the devil, with Tonya Welton, in order to make it happen?

Well, at any rate, he had managed to steer things away from any discussion of the Three Laws. If he had been forced to sacrifice a few tidbits about gravitonics in order to accomplish that, so be it. It would all be public in a day or so, anyway.

They were safe for the moment. But still, the project was madness. Caliban was madness. Building him had been a violation of the most basic Spacer law and philosophy, but Fredda Leving had gone ahead, anyway. Typical bullheadedness.

Never mind theory and philosophy, she had said. They were an experimental lab, not a theory shop that never acted on its ideas. It was time to take the next step, she said. It was time to build a gravitonic robot with no limits on its mind whatsoever. A blank slate, that's what she had called Caliban. An experimental robot, to be kept inside the lab at all times, never to leave. A robot with no knowledge of other robots, or the Settlers, or anything beyond human behavior and a carefully edited source of knowledge about the outside world. Then let it live at the lab, under controlled conditions, and see what happens. See what rules it developed for its own behavior.

Did she truly have to build Caliban?

No, ask the question directly,he told himself.We've all hedged around it long enough. And yes, that was the deadly secret question. No one else knew. With Caliban broken free of the lab, with Fredda unconscious, there was no one else in the wide world who could ask the question.

So Jomaine asked it of himself.

Did she really have to build a robot that did not have the Three Laws?