The V-frog's plastic cage was shattered and shriveled, and the floor was wet with its watery contents. The V-frog, half covered with the fronds it fed upon, was quite, quite dead.

Now that it was dead and unable to control emotion, Lucky could look at it without the enforced fondness that he, as well as all others that came within its radius of influence, had felt. He felt anger, however-mostly at himself for having allowed himself to be overreached.

Bigman, fresh from his shower, with only his shorts on, clenched and unclenched his fists. "It's my fault, Lucky. It's all my fault. I was yelling so loud in the shower I never heard anyone come in."

The phrase "come in" was not quite appropriate. The killer had not simply come in; he had burnt his way in. The lock controls were fused and melted away with what had obviously been an energy projector of fairly large caliber.

Lucky stepped back to the interphone. "Commander Donahue?"

"Yes, what happened? Is anything wrong?" "I'll see you in an hour." He broke connections and returned to the grieving Bigman. He said somberly, "It's my fault, Bigman. Uncle Hector said the Sirians had not yet discovered the facts concerning the emotional powers of the V-frog, and I accepted that too thoroughly. If I had been a little less optimistic about Sirian ignorance, neither one of us would ever have left that little creature out of our sight for a second."

Lieutenant Nevsky called for them, standing at attention as Lucky and Bigman left their quarters.

He said in a low voice, "I am glad, sir, that you were unharmed in yesterday's encounter. I would not have left you, sir, had you not strictly ordered me to."

"Forget it, Lieutenant," Lucky said absently. His mind kept returning to that moment just before sleep the preceding night when, for a brief instant, a thought had hovered at the outskirts of consciousness, then vanished. But it would not come now, and finally Lucky's mind sped to other matters.

They had entered the Agrav corridor now, and this time it seemed crowded with men, streaming accurately and unconcernedly in both directions. There was a "beginning of the work day" atmosphere all about. Though men worked underground here and there was no day or night, yet the old twenty-four-hour schedule held. Mankind brought the familiar rotation of the Earth to all the worlds on which he lived. And though men might work in shifts the clock round, the largest number always worked on the "day shift" from nine to five, Solar Standard Time.

It was nearly nine now, and there was a bustle through the Agrav corridors as men traveled to the work posts. There was a feel of "morning" almost as strong as though there were a sun low in the eastern sky and dew on the grass.

Two men were sitting at the table when Lucky and Bigman entered the conference room. One was Commander Donahue, whose face bore the appearance of a carefully controlled tension. The commander rose and coldly introduced the other: James Panner, the chief engineer and civilian head of the project. Panner was a stocky man with a swarthy face, dark deep-set eyes, and a bull neck. He wore a dark shirt open at the collar and without insignia of any sort.

Lieutenant Nevsky saluted and retired. Commander Donahue watched the door close and said, "Since that leaves the four of us, let's get to business."

"The four of us and a cat," said Lucky, stroking a small creature that hitched its forepaws on the table and stared at him solemnly. "This isn't the same cat I saw yesterday, is it?"

The commander frowned. "Perhaps. Perhaps not. We have a number of cats on the satellite. However, I presume we're not here to discuss pets."

Lucky said, "On the contrary, Commander, I think it will do as a topic of conversation to begin with and I chose it deliberately. Do you remember my own pet, sir?"

"Your little Venusian creature?" said the commander with sudden warmth. "I remember it. It was-" He stopped in confusion as though wondering, in the V-frog's absence, what the reason for his enthusiasm concerning it might be

"The little Venusian creature," said Lucky, "had peculiar abilities. It could detect emotion. It could transmit emotion. It could even impose emotion."

The commander's eyes opened wide, but Panner said in a husky voice, "I once heard a rumor to that effect, Councilman. I laughed."

"You needn't have. It is true. In fact, Commander Donahue, my purpose in asking for this interview was to make arrangements to have every man on the project interviewed by me in the presence of the V-frog. I wanted an emotional analysis."

The commander still seemed half stunned. "What would that prove?"

"Perhaps nothing. Still, I meant to try it."

Panner intervened. "Meant to try it? You use the past tense, Councilman Starr."

Lucky stared solemnly at the two project officials. "My V-frog is dead."

Bigman said furiously, "Killed this morning."

The commander said, "Who killed it?"

"We don't know, Commander."

The commander sat back in his chair. "Then your little investigation is over, I suppose, till the animal can be replaced."

Lucky said, "There will be no waiting. The mere fact of the V-frog's death has told me a great deal, and the matter becomes much more serious."

"What do you mean?"

All stared. Even Bigman looked up at Lucky in profound surprise.

Lucky said, "I told you that the V-frog has the capacity to impose emotion. You yourself, Commander Donahue, experienced that. Do you recall your feelings when you saw the V-frog on my ship yesterday? You were under considerable strain, yet when you saw the V-frog- Do you remember your feelings, sir?"

"I was rather taken with the creature," the commander faltered.

"Can you think why, as you look back at the moment now?"

"No, come to think of it. Ugly creature."

"Yet you liked it. You couldn't help yourself. Could you have harmed it?"

"I suppose not."

"I'm certain you couldn't. No one with emotions could have. Yet someone did. Someone killed it."

Panner said, "Do you intend to explain the paradox?"

"Easily explained. No one with emotions, A robot, however, does not have emotions. Suppose that somewhere on Jupiter Nine there is a robot, a mechanical man, in the perfect form of a human being?"

"You mean a humanoid?" exploded Commander Donahue. "Impossible. Such things exist only in fairy tales."

Lucky said, "I think, Commander, you are not aware of how skillful the Sirians are in the manufacture of robots. I think they might be able to use some man on Jupiter Nine, some thoroughly loyal man, as model; build a robot in his shape and substitute it for him. Such a humanoid robot could have special senses that would enable it to be the perfect spy. It might, for instance, be able to see in the dark or sense things through thicknesses of matter. It would certainly be able to transmit information through the subether by some built-in device."

The commander shook his head. "Ridiculous. A man could easily have killed the V-frog. A desperate man frightened to an extreme might have overcome this- this mental influence the animal exerted. Have you thought of that?"

"Yes, I have," said Lucky. "But why should a man be so desperate, why so wild to kill a harmless V-frog? The most obvious reason is that the V-frog represented a desperate danger, that it was not harmless at all. The only danger a V-frog might have to the killer would involve the animal's capacity to detect and transmit the killer's emotions. Suppose those emotions would be an immediate giveaway to the fact that the killer was a spy?"

"How could it be?" Panner asked.

Lucky turned to look at him. "What if our killer had no emotions at all? Wouldn't a man without emotions be revealed at once as a robot?... Or take it another way altogether. Why kill only the V-frog? Having gotten into our rooms, having risked so much, having found one of us in the shower and one at the intercom and both unsuspecting and unready, why did not the killer kill us instead of the V-frog? For that matter, why not kill us and the V-frog?"

"No time, probably," said the commander.

"There's another and more plausible reason," said Lucky. "Do you know the Three Laws of Robotics, the rules of behavior that all robots are built to follow?"

"I know them generally," the commander said. "I can't quote them."

"I can," said Lucky, "and with your permission I will, so that I may make a point. The First Law is this: A robot may not injure a human being or, through inaction, allow a human being to come to harm. The Second Law is: A robot must obey the orders given it by human beings except where such orders would conflict with the First Law. The Third Law is: A robot must protect its own existence as long as such protection does not conflict with the First or Second Law."

Panner nodded. "All right, Councilman, what does that prove?"

"A robot can be ordered to kill the V-frog, which is an animal. It will risk its existence, since self-preservation is only Third Law, to obey orders, which is Second Law. But it cannot be ordered to kill Bigman or myself, since we are humans, and First Law takes precedence over all. A human spy would have killed us and the V-frog; a robot spy would have killed only the V-frog. It all points to the same thing, Commander."

The commander considered that for long minutes, sitting motionless, the lines on his tired face grooving deeper. Then he said, "What do you propose to do? X-ray every man on the project?"

"No," said Lucky at once. "It's not that simple. Successful espionage is going on elsewhere than here. If there is a humanoid robot here, there are probably others elsewhere. It would be well to catch as many of the humanoids as possible; all of them if we can. If we act too eagerly and openly to catch the one under our hands, the others may be snatched away for use at another time."

"Then what do you propose doing?"

"To work slowly. Once you suspect a robot, there are ways of making it give itself away without its being aware of it. And I don't start completely from scratch. For instance, Commander, I know you are not a robot, since I detected emotion in you yesterday. In fact, I deliberately induced anger in you to test my V-frog, and for that I ask your pardon."

Donahue's face had gone mauve. "I, a robot?"

"As I said, I used you only to test my V-frog."

Panner said dryly, "You have no reason to feel sure about me, Councilman. I never faced your V-frog."

"That is right," said Lucky. "You are not cleared yet. Remove your shirt."

"What!" cried Panner indignantly. "Why?"

Lucky said mildly, "You have just been cleared. A robot would have had to obey that order."

The commander's fist banged down on his desk. "Stop it! This ends right here. I will not have you testing or annoying my men in any way. I have a job to do on this satellite, Councilman Starr; I have an Agrav ship to get into space, and I'm getting it into space. My men have been investigated and they're clear. Your story about a robot is flimsy, and I'm not going along with it.

"I told you yesterday, Starr, that I didn't want you on this satellite disturbing my men and wrecking their morale. You saw fit yesterday to address me in insulting fashion. You say now it was just to test your animal, which makes it no less insulting. For that reason, I feel no need to co-operate with you and I am not doing so. Let me tell you exactly what I have done.

"I've cut off all communication with Earth. I've put Jupiter Nine under emergency orders. I have the powers of a military dictator now. Do you understand?"

Lucky's eyes narrowed a trifle. "As councilman of the Council of Science, I outrank you."

"How do you intend to enforce your rank? My men will obey me and they have their orders. You will be restrained forcibly if you try in any way, by word or deed, to interfere with my orders."

"And what are your orders?"

"Tomorrow," said Commander Donahue, "at 6 p.m., Solar Standard Time, the first functioning Agrav ship in existence will make its first flight from Jupiter Nine to Jupiter One, the satellite lo. After we're back- after we're back, Councilman Starr, and not one hour sooner-you may conduct your investigation. And if you then want to get in touch with Earth and arrange court-martial proceedings, I will be ready for you."

Commander Donahue stared firmly at Lucky Starr.

Lucky said to Panner, "Is the ship ready?"

PFanner said, "I think so."

Donahue said scornfully. "We leave tomorrow. Well, Councilman Starr, do you go along with me or will I have to have you arrested?"

The silence that followed was a tense one. Bigman virtually held his breath. The commander's hands were clenching and unclenching, and his nose was white and pinched. Panner slowly fumbled a stick of gum out of his shirt pocket, stripped it of its plastofoil coating with one hand, and crumpled it into his mouth.

And then Lucky clasped his hands loosely, sat back in his chair, and said, "I'll be glad to co-operate with you, Commander."