“Granted,” said Baley. “I am only an Earthman. I know next to nothing about robots and my phrasing of the orders was only by way of example. A Solarian would be much more subtle and do much better. I’m sure of that.”

Leebig might not have been listening. He said loudly, “If a robot

can be manipulated into doing harm to a man, it means only that we must extend the powers of the positronic brain. One might say we ought to make the human better. That is impossible, so we will make the robot more foolproof.

“We advance continuously. Our robots are more varied, more specialized, more capable, and more unharming than those of a century ago. A century hence, we will have still greater advances. Why have a robot manipulate controls when a positronic brain can be built into the controls itself? That’s specialization, but we can generalize, also. Why not a robot with replaceable and interchangeable limbs. Eh? Why not? If we—”

Baley interrupted. “Are you the only roboticist on Solaria?”

“Don’t be a fool.”

“I only wondered. Dr. Delmarre was the only—uh—fetal engineer, except for an assistant.”

“Solaria has over twenty roboticists.”

“Are you the best?”

“I am,” Leebig said without self-consciousness.

“Delmarre worked with you.”

“He did.”

Baley said, “I understand that he was planning to break the partnership toward the end.”

“No sign of it. What gave you the idea?”

“I understand he disapproved of your bachelorhood.”

“He may have. He was a thorough Solarian. However, it did not affect our business relationships.”

“To change the subject. In addition to developing new model robots, do you also manufacture and repair existing types?”

Leebig said, “Manufacture and repair are largely robot conducted. There is a large factory and maintenance shop on my estate.”

“Do robots require much in the way of repair, by the way?”

“Very little.”

“Does that mean that robot repair is an undeveloped science?”

“Not at all.” Leebig said that stiffly.

“What about the robot that was at the scene of Dr. Delmarre’s murder?”

Leebig looked away, and his eyebrows drew together as though a painful thought were being barred entrance to his mind. “It was a complete loss.”

“Really complete? Could it answer any questions at all?”

“None at all. It was absolutely useless. Its positronic brain was completely short-circuited. Not one pathway was left intact. Consider! It had witnessed a murder it had been unable to halt—”

“Why was it unable to halt the murder, by the way?”

“Who can tell? Dr. Delmarre was experimenting with that robot. I do not know in what mental condition he had left it. He might have ordered it, for instance, to suspend all operations while he checked one particular circuit element. If someone whom neither Dr. Delmarre nor the robot suspected of harm were suddenly to launch a homicidal attack, there might be a perceptible interval before the robot could use First Law potential to overcome Dr. Delmarre’s freezing order. The length of the interval would depend on the nature of the attack and the nature of Dr. Delmarre’s freezing order. I could invent a dozen other ways of explaining why the robot was unable to prevent the murder. Being unable to do so was a First Law violation, however, and that was sufficient to blast every positronic pathway in the robot’s mind.”

“But if the robot was physically unable to prevent the murder, was it responsible? Does the First Law ask impossibilities?”

Leebig shrugged. “The First Law, despite your attempts to make little of it, protects humanity with every atom of possible force. It allows no excuses. If the First Law is broken, the robot is ruined.”

“That is a universal rule, sir?”

“As universal as robots.”

Baley said, “Then I’ve learned something.”

“Then learn something else. Your theory of murder by a series of robotic actions, each innocent in itself, will not help you in the case of Dr. Delmarre’s death.”

“Why not?”

“The death was not by poisoning, but by bludgeoning. Something had to hold the bludgeon, and that had to be a human arm. No robot could swing a club and smash a skull.”

“Suppose,” said Baley, “a robot were to push an innocent button which dropped a booby-trap weight on Delmarre’s head.”

Leebig smiled sourly. “Earthman, I’ve viewed the scene of the crime. I’ve heard all the news. The murder was a big thing here on Solaria, you know. So I know there was no sign of any machinery at the scene of the crime, or of any fallen weight.”

Baley said, “Or of any blunt instrument, either.” Leebig said scornfully, “You’re a detective. Find it.”

“Granting that a robot was not responsible for Dr. Delmarre’s death, who was, then?”

“Everyone knows who was,” shouted Leebig. “His wife! Gladia!” Baley thought: At least there’s a unanimity of opinion. Aloud he said, “And who was the mastermind behind the robots who poisoned Gruer?”

“I suppose…” Leebig trailed off.

“You don’t think there are two murderers, do you? If Gladia was responsible for one crime, she must be responsible for the second attempt, also.”

“Yes. You must be right.” His voice gained assurance. “No doubt of it.”

“No doubt?”

“Nobody else could get close enough to Dr. Delmarre to kill him. He allowed personal presence no more than I did, except that he made an exception in favor of his wife, and I make no exceptions. The wiser I.” The roboticist laughed harshly.

“I believe you knew her,” said Baley abruptly.

“Whom?”

“Her. We are discussing only one ‘her.’ Gladia!”

“Who told you I knew her any more than I know anyone else?” demanded Leebig. He put his hand to his throat. His fingers moved slightly and opened the neck seam of his garment for an inch downward, leaving more freedom to breathe.

“Gladia herself did. You two went for walks.”

“So? We were neighbors. It is a common thing to do. She seemed a pleasant person.”

“You approved of her, then?”

Leebig shrugged. “Talking to her was relaxing.”

“What did you talk about?”

“Robotics.” There was a flavor of surprise about the word as though there were wonder that the question could be asked.

“And she talked robotics too?”

“She knew nothing about robotics. Ignorant! But she listened. She has some sort of field-force rigmarole she plays with; field coloring, she calls it. I have no patience with that, but I listened.”

“All this without personal presence?” Leebig looked revolted and did not answer. Baley tried again, “Were you attracted to her?”

“What?”

“Did you find her attractive? Physically?”

Even Leebig’s bad eyelid lifted and his lips quivered. “Filthy animal,” he muttered.

“Let me put it this way, then. When did you cease finding Gladia pleasant? You used that word yourself, if you remember.”

“What do you mean?”

“You said you found her pleasant. Now you believe she murdered her husband. That isn’t the mark of a pleasant person.”

“I was mistaken about her.”

“But you decided you were mistaken before she killed her husband, if she did so. You stopped walking with her some time before the murder. Why?”

Leebig said, “Is that important?”

“Everything is important till proven otherwise.”

“Look, if you want information from me as a roboticist, ask it. I won’t answer personal questions.”

Baley said, “You were closely associated with both the murdered man and the chief suspect. Don’t you see that personal questions are unavoidable? Why did you stop walking with Gladia?”

Leebig snapped, “There came a time when I ran out of things to say; when I was too busy; when I found no reason to continue the walks.”

“When you no longer found her pleasant, in other words.”

“All right. Put it so.”

“Why was she no longer pleasant?”