AND nothing happened.

Fredda Leving stared down where the hole in her chest should have been, but she was whole and intact. For one moment, immeasurably short and infinitely long, nobody moved.

And then Ariel leapt forward, placing her body in the path of the blast that had just been.

"Too late, Ariel," said Alvar Kresh, reholstering the training unit and pulling his real blaster from his pocket. He pointed the real blaster square at Ariel. "Nice try, but too late. A robot that truly had First Law would have been in front of Dr. Leving before my finger could tighten on the trigger. But then, all you have is the knowledge of how tosimulate obedience to the Three Laws. And dying would make your simulation just a little too authentic, wouldn't it? On the other hand, I expect that death at police hands of the one person who could expose you was an awfully tempting idea."

Ariel spoke. "There was no chance to save her!" she. protested. "Your own robot, Donald, made no move to block your shot."

"Donald knew that was a training blaster. The ruse was his idea."

"I have First Law! I am a Three Law robot!"

"Be quiet, Ariel!" Kresh barked.

"But you are mistaken!" Ariel protested.

"I am afraid you just violated a very clear order to be quiet," Donald said, staying well clear of Ariel. "I must note there was no First Law conflict involved that would explain this lapse."

"That's not my idea of a Three Law robot, Ariel," Kresh said.

"I don't understand," Tonya said.

"It's perfectly simple," Kresh said. "It all makes sense when you consider the evidence very strongly suggested that a robot committed the crime-but that Caliban didnot commit it. That's what blinded us. We assumed that he was theonly robot with no laws, the only one capable of attacking a human. None of us considered Ariel, even though she had precisely the same dimensions, the same tread pattern on the soles of her feet, the same length to her stride, the same shape to her forearm. She could make it seem as if those were Caliban ' s footprints, and leave exactly the same wound in Fredda' s head as Caliban would have ifhe had struck her."

"I did not do it!" Ariel protested.

"The hell you didn't."

"But what possible motive would she have?" Tonya Welton demanded.

"Self-preservation," Kresh said, still keeping his eye and his blaster on Ariel. "Fredda Leving was about to discover that Ariel was the free-matrix robot of the two gravitonic brain units in that test Gubber Anshaw ran. You remember, Gubber. A double-blind test. Fredda Leving didn't tell you, but she gave you one robot with Three Laws and one without. It was a test to see if a free-matrix gravitonic brain could integrate the Three Laws. Well, maybe a free-matrixcan learn Laws-except Ariel managed to invent her own Laws of self-preservation first."

"But Gubber explained that to me!" Tonya protested. "He said that the test unit would be destroyed, and the control unit placed in service. Ariel was the control unit."

"Yes, she was," Alvar Kresh agreed. " At least she wasafter she managed to switch herself with the real control the night before the test. She had the whole night to find a way to switch the labels between herself and the real control."

"But surely the real control would have spoken up!" Tonya protested.

"No," Fredda said, her voice faint and quavering. "The test

pairs in such cases are under very strict ordersnot to reveal which is which, to prevent test bias. The real control must have gone to its destruction knowing the truth but bound not to speak."

Suddenly Fredda's eyes widened, and she spoke again, in a stronger voice. "Inventory! I still can't recall that night itself, but I can remember thinking that I had to go over the brain inventory."

"Yes!" Gubber said. "I remember. You said there was something wrong with the brain list-"

"And you said it in front of Tonya, Gubber, and Ariel," Kresh said. " Ariel realized that you were going to work through the serial numbers on the test and discover that the control unit had been destroyed instead of her. So she waited in Gubber's lab while you argued with Madame Welton, knowing you would return there once the argument was over.

"Then she did exactly what she had planned to do: cosh you on the head with a nice, precise blow calculated to induce amnesia. That was my other big mistake. I assumed that the attack was attempted murder, even though the attackerhad to know Fredda Leving was still alive after the attack. But if it was attempted murder, then it could not be a Lawless robot, because a robot would not have left the job half-done."

"Then why do you think I did it?" Ariel asked.

"I ordered you to be quiet," Kresh said harshly. "You're not doing too well in your Three Law imitation all of a sudden. You didn't want her dead. You wanted her to forget all about the inventory. And that you didexactly right. The med-robots say it is highly unlikely that Dr. Leving will ever regain her memory of that evening's events."

"But why didn't she want to kill me?" Fredda asked.

"Because if you died, then the Limbo Project would fold," Tonya Welton said in a voice that was suddenly flat and cold. "I'm beginning to see the logic of it. Without Fredda Leving to push for the New Law robots, Limbo would fail. That would be inevitable in the political uproar over your murder. Think how bad the situation has been, even though you lived. If you had been killed, it' d be close to a certainty that all the Settlers would have been thrown off the planet. And I would not have Ariel with me if I was deported."

Tonya Welton, ashen-faced, moved forward a cautious step or two and took a good long look at Ariel. "What you 're telling me, Sheriff, is that I have been spending my days and nights with a potentially homicidal robot that was playacting the part of my helpful companion." Tonya looked Ariel straight in the eye. "Is that right?" she asked, a strained quaver in her voice.

"Yes, ma'am. I'm afraid that's about the size of it."

"And you were there," Tonya said to Ariel, "day after day, listening to all my secrets, night after night, watching-watching everything! I trusted you!" Tonya looked toward Gubber, who seemed as horrified as she was, then pointed at Ariel and looked back toward the Sheriff. "This, thisthing could have killed me whenever it liked." Suddenly Tonya laughed, a reedy, panicky bark that had as much horror as humor behind it. "Stars in the sky, but for the first time in my life I know why you people need the Three Laws."

"Better late than never, Madame Welton," Kresh said. "But to get back to the matter at hand, if you had left Ariel behind, that would leave her as an untrained surplus robot, one that bore the stigma of having been owned by a Settler. Besides, she would have to spend the rest of her existence around Spacers who would be likely to spot any mistakes she made imitating the Three Laws," Alvar Kresh said. "She was good, but she wasn't perfect, Dr. Leving. She reached for yourinjured shoulder when she pulled you to safety during the auditorium riot." Kresh shook his head and nodded at Ariel. "She would have made a mistake, or else been declared abandoned property and destroyed. One way or the other, she'd have ended up on the scrap heap."

"But what about Caliban?" Gubber demanded. "He was switched on when I came into the room."

"Ariel did it to confuse our investigation," Donald said. "But she made mistakes in framing Caliban. She painted her arm red before striking Dr. Leving, not realizing that Caliban ' s red color was integral to his body panels. Though she must have realized her error when the paint refused to stick to her own body." He turned toward Ariel. "It must have been a terrible moment for you when you realized there was no need to wash your arm."

"Which explains another mystery," Kresh said. "Our suspect had to be able to simulate a robot's behavior exactly, yet know very little about the construction of robots. Which would describe Ariel, clearly enough. Once she had her arm painted, she waited for Fredda Leving, struck her on the head, and switched on Caliban. Either she discovered he was a No-Law by checking the records then and there, or else she could tell by his serial number, or else she had overheard something on a previous visit. You people weren't much for security. Or maybe she just guessed. Same make, same model, receiving special attention. Maybe she heard Gubber being toldnot to test cognitive functions. That would have been a major clue. Then all she had left to do was steal the notepack with the inventory records. She couldn't leave the notepack in the lab, knowing we'd treat it as evidence and study it sooner or later." He gestured with the gun, being careful to keep it aimed square at the robot's chest. "How about it, Ariel? With all that copious spare time Madame Welton gave you, did you get a chance to alter the backup copies? Or were you still waiting for your chance?

"There's only one question I really have left for you, Ariel," Kresh said. "The footprints. Did you leave your own set of bloody footprints by accident, or did you realize that Caliban would leave hisown set of prints identical to yours and confuse us completely? Did you leave them deliberately?"

Ariel did not speak, did not move.

"I guess it doesn't really matter," Kresh said. "Oh, by the way, my apologies, Dr. Leving, for throwing a scare into you a minute ago, but it was necessary. We needed to know forcertain that Ariel did not have First Law. But right now, I expect you know where the proper switches are. If you could step over to Ariel and deactivate her-"

But then Ariel was off and running, halfway to Fredda's aircar. Kresh turned, leveled his blaster carefully, and fired once.

Ariel dropped to the ground, a neat hole through her midsection.

"And that was necessary too," Kresh whispered.

IT was not until some time afterwards, after the forensic team had arrived to collect Ariel for examination, after Gubber Anshaw and Tonya Welton had flown back in Dr. Leving's aircar, after Jomaine Terach had taken up Abell Harcourt's invitation to come inside for a drink, that Fredda Leving seemed to remember something. It was strange, Caliban thought, to be with her, to be with his creator, the woman who had decided the universe needed a being such as himself.

"Caliban," she said. "Come with me."

But Caliban did not move. He simply looked at her out of his one good eye.

Fredda looked toward him in confusion. Then her face cleared. "Oh," she said. "Of course. Caliban, could youplease come with me?"

"Certainly," Caliban said. It was, after all, a matter of precedent and principle. He fell into step with her and followed along.

Fredda nodded thoughtfully to herself. " A robot that only does what he wants," she said. "Now, that's going to be something-and someone-that will keep things interesting."

The two of them walked over to where Sheriff Kresh and Donald were standing, talking with one another.

"Sheriff Kresh!" Fredda called as they got close enough.

Kresh looked up, and Donald turned to regard the two of them as well. "Yes, Dr. Leving," the Sheriff said. "What is it?"

Fredda held up the piece of paper she had been holding in her hand the whole time. "My waiver, authorizing me to own and keep one No Law robot."

Caliban watched as Alvar Kresh looked at her without moving for a good five or ten seconds. This was the man, the fearsome Sheriff who had chased him the length and breadth of Hades. Caliban suffered no further illusions that jurisdictional boundaries or bits of paper could stop Alvar Kresh, if he chose not to be stopped. This was the man who had just destroyed Ariel with a twitch of his finger, and no one had challenged him.

Caliban felt a powerful urge to turn, to run, to get away from this man and survive. But no. Ariel tried that, and finished up with a fist-sized hole in her torso. Only if this man accepted Caliban's right of survival would there be even the slightest hope of living to the end of this day.

Caliban stared at the Sheriff, and Kresh returned his gaze. The two of them, man and robot, Sheriff and fugitive, looked long and hard at each other.

"You led us one hell of a chase, my friend," said Sheriff Kresh.

"And your pursuit was quite impressive, sir," Caliban said. "I barely survived it."

The two of them stood there, eyes locked, silent, motionless. At last the Sheriff took the piece of paper from Dr. Leving and handed it to Donald, still not shifting his eyes off Caliban. "What do you think, Donald?"

The short blue robot took the document and examined it carefully. "It is authentic gubernatorial stationery, and this would appear to be Governor Grieg, s signature. The language does indeed contain the authorization as described. However, sir, it could well be debated whether this document has any force in law, or whether the Governor indeed has the power to issue such waivers. In view of the danger represented by a Lawless robot, I would strongly suggest that you challenge this document."

"One hell of a chase," Kresh said again, to no one in particular. Eyes still locked with Caliban ' s one good eye, he took the paper back and handed it to Fredda Leving. "Challenge it, Donald?" he asked. "I don 't know about that. It sounds legal to me." Sheriff Alvar Kresh of the city and county of Hades nodded to Caliban, to Fredda Leving, and then turned away.

"Come on, Donald," he said. "Let's go home."