“But we had to have robots of a different nature. So just a few of the NS-2 model, the Nestors, that is, were prepared with a modified First Law. To keep it quiet, all NS-2’s are manufactured without serial numbers; modified members are delivered here along with a group of normal robots; and, of course, all our kind are under the strictest impressionment never to tell of their modification to unauthorized personnel.” He wore an embarrassed smile; “This has all worked out against us now.”

Calvin said grimly, “Have you asked each one who it is, anyhow? Certainly, you are authorized?”

The general nodded, “All sixty-three deny having worked here – and one is lying.”

“Does the one you want show traces of wear? The others, I take it, are factory-fresh.”

“The one in question only arrived last month. It, and the two that have just arrived, were to be the last we needed. There’s no perceptible wear.” He shook his head slowly and his eyes were haunted again, “Dr. Calvin, we don’t dare let that ship leave. If the existence of non-First Law robots becomes general knowledge-” There seemed no way of avoiding understatement in the conclusion.

“Destroy all sixty-three,” said the robopsychologist coldly and flatly, “and make an end of it.”

Bogert drew back a corner of his mouth. “You mean destroy thirty thousand dollars per robot. I’m afraid U. S. Robots wouldn’t like that. We’d better make an effort first, Susan, before we destroy anything.”

“In that case,” she said, sharply, “I need facts. Exactly what advantage does Hyper Base derive from these modified robots? What factor made them desirable, general?”

Kallner ruffled his forehead and stroked it with an upward gesture of his hand. “We had trouble with our previous robots. Our men work with hard radiations a good deal, you see. It’s dangerous, of course, but reasonable precautions are taken. There have been only two accidents since we began and neither was fatal. However, it was impossible to explain that to an ordinary robot. The First Law states – I’ll quote it – ‘No robot may harm a human being, or through inaction, allow a human being to come to harm.’

“That’s primary, Dr. Calvin. When it was necessary for one of our men to expose himself for a short period to a moderate gamma field, one that would have no physiological effects, the nearest robot would dash in to drag him out. If the field were exceedingly weak, it would succeed, and work could not continue till all robots were cleared out. If the field were a trifle stronger, the robot would never reach the technician concerned, since its positronic brain would collapse under gamma radiations – and then we would be out one expensive and hard-to-replace robot.

“We tried arguing with them. Their point was that a human being in a gamma field was endangering his life and that it didn’t matter that he could remain there half an hour safely. Supposing, they would say, he forgot and remained an hour. They couldn’t take chances. We pointed out that they were risking their lives on a wild off-chance. But self-preservation is only the Third Law of Robotics – and the First Law of human safety came first. We gave them orders; we ordered them strictly and harshly to remain out of gamma fields at whatever cost. But obedience is only the Second Law of Robotics – and the First Law of human safety came first. Dr. Calvin, we either had to do without robots, or do something about the First Law – and we made our choice.”

“I can’t believe,” said Dr. Calvin, “that it was found possible to remove the First Law.”

“It wasn’t removed, it was modified,” explained Kallner. “Positronic brains were constructed that contained the positive aspect only of the Law, which in them reads: ‘No robot may harm a human being.’ That is all. They have no compulsion to prevent one coming to harm through an extraneous agency such as gamma rays. I state the matter correctly, Dr. Bogert?”

“Quite,” assented the mathematician.

“And that is the only difference of your robots from the ordinary NS2 model? The only difference? Peter?”

“The only difference, Susan.”

She rose and spoke with finality, “I intend sleeping now, and in about eight hours, I want to speak to whomever saw the robot last. And from now on, General Kallner, if I’m to take any responsibility at all for events, I want full and unquestioned control of this investigation.”

Susan Calvin, except for two hours of resentful lassitude, experienced nothing approaching sleep. She signaled at Bogert’s door at the local time of 0700 and found him also awake. He had apparently taken the trouble of transporting a dressing gown to Hyper Base with him, for he was sitting in it. He put his nail scissors down when Calvin entered.

He said softly, “I’ve been expecting you more or less. I suppose you feel sick about all this.”

“I do.”

“Well – I’m sorry. There was no way of preventing it. When the call came out from Hyper Base for us, I knew that something must have gone wrong with the modified Nestors. But what was there to do? I couldn’t break the matter to you on the trip here, as I would have liked to, because I had to be sure. The matter of the modification is top secret.”

The psychologist muttered, “I should have been told. U. S. Robots had no right to modify positronic brains this way without the approval of a psychologist.”

Bogert lifted his eyebrows and sighed. “Be reasonable, Susan. You couldn’t have influenced them. In this matter, the government was bound to have its way. They want the Hyperatomic Drive and the etheric physicists want robots that won’t interfere with them. They were going to get them even if it did mean twisting the First Law. We had to admit it was possible from a construction standpoint and they swore a mighty oath that they wanted only twelve, that they would be used only at Hyper Base, that they would be destroyed once the Drive was perfected, and that full precautions would be taken. And they insisted on secrecy – and that’s the situation.”

Dr. Calvin spoke through her teeth, “I would have resigned.”

“It wouldn’t have helped. The government was offering the company a fortune, and threatening it with antirobot legislation in case of a refusal. We were stuck then, and we’re badly stuck now. If this leaks out, it might hurt Kallner and the government, but it would hurt U. S. Robots a devil of a lot more.”

The psychologist stared at him. “Peter, don’t you realize what all this is about? Can’t you understand what the removal of the First Law means? It isn’t just a matter of secrecy.”

“I know what removal would mean. I’m not a child. It would mean complete instability, with no nonimaginary solutions to the positronic Field Equations.”

“Yes, mathematically. But can you translate that into crude psychological thought. All normal life, Peter, consciously or otherwise, resents domination. If the domination is by an inferior, or by a supposed inferior, the resentment becomes stronger. Physically, and, to an extent, mentally, a robot – any robot – is superior to human beings. What makes him slavish, then? Only the First Law! Why, without it, the first order you tried to give a robot would result in your death. Unstable? What do you think?”

“Susan,” said Bogert, with an air of sympathetic amusement. “I’ll admit that this Frankenstein Complex you’re exhibiting has a certain justification – hence the First Law in the first place. But the Law, I repeat and repeat, has not been removed – merely modified.”

“And what about the stability of the brain?”

The mathematician thrust out his lips, “Decreased, naturally. But it’s within the border of safety. The first Nestors were delivered to Hyper Base nine months ago, and nothing whatever has gone wrong till now, and even this involves merely fear of discovery and not danger to humans.”

“Very well, then. We’ll see what comes of the morning conference.”