But even as Bigman felt his stomach constrict at the prospect of imminent destruction, he could hear Lucky's even voice speaking forcefully into the transmitter:

"Subship Hilda arriving with cargo of petroleum... Subship Hilda arriving with cargo of petroleum... Subship Hilda arriving with cargo of petroleum... Subship Hilda..."

An agitated voice broke through from the other end. "Clement Heber at lock control at this end. What is wrong? Repeat. What is wrong? Clement Heber..."

Bigman yelled, "They're withdrawing the blaster, Lucky."

Lucky let out his breath in a puff, but only in that way did he show any sign of tension. He said into the transmitter, "Subship Hilda reporting for entrance to Aphrodite. Please assign lock. Repeat. Please assign lock."

"You may have lock number fifteen. Follow directional signal. There seems to be some confusion here."

Lucky rose and said to Evans, "Lou, take the controls and get the ship into the city as fast as you can." He motioned Bigman to follow him to the other room.

"What-what..." Bigman spluttered like a leaky

popgun.

Lucky sighed and said, "I thought the V-frogs would try to arrange to have us kept out, so I was all set with the petroleum trick. But I didn't think things would get so bad they would point a cannon at us. That made it really tough. I wasn't as sure as all that that the petroleum notion would work."

"But how did it?"

"Hydrocarbon again. Petroleum is hydrocarbon. My word came over the open radio and the V-frogs who had the dome guards under control were distracted."

"How come they knew what petroleum was?"

"I pictured it in my mind, Bigman, with every bit of imagination I had. They can read minds when you sharpen the mental pictures by speaking, you know.

"But never mind all that." His voice dropped to a whisper. "If they're ready to blow us out of the ocean, if they're ready for something as crudely violent as that, they're desperate; and we're desperate, too. We've got to bring this to an end right away, and we've got to do the right thing. One mistake at this stage could be fatal."'

From his shirt pocket Lucky had undipped a scriber, and he was writing rapidly on a piece of foil.

He held it out to Bigman. "That's what you're to do when I give the word."

Bigman's eyes widened, "But Lucky..."

"Sh! Don't refer to any of this in words."

Bigman nodded, "But are you sure you're right?"

"I hope so." Lucky's handsome face was drawn with anxiety. "Earth knows about the V-frogs now, so they'll never win over humanity; but they may still do damage here on Venus. We've got to prevent that somehow. Now do you understand what you're to do?"

"Yes."

"In that case..." Lucky rolled the foil together and kneaded it with his strong fingers. The pellet that remained he returned to his shirt pocket.

Lou Evans called out, "We're in the lock, Lucky. In five minutes we'll be in the city."

Lucky said, "Good. Get Morriss on the radio."

They were in Council headquarters in Aphrodite again, the same room, Bigman thought, in which he had first met Lou Evans; the same room in which he had first seen a V-frog. He shuddered at the thought of those mental tendrils infiltrating his mind for the first time without his knowledge.

That was the one way in which the room was different now. The aquarium was gone; the dishes of peas and of axle grease were gone; the tall tables stood bare at the false window.

Morriss had pointed that out mutely as soon as they entered. His plump cheeks sagged and the lines of strain about his eyes were marked. His pudgy handshake was uncertain.

Carefully Bigman put what he was carrying on top of one of the tables. "Petroleum jelly," he said.

Lou Evans sat down. So did Lucky.

Morriss did not. He said, "I got rid of the V-frogs in this building. That was all I could do. I can't ask people to do away with their pets without a reason. And I couldn't give the reason, obviously."

"It will be enough," said Lucky. "Throughout this discussion, though, I want you to keep your eyes on the hydrocarbon. Keep its existence firmly in your mind."

"You think that will help?" asked Morriss.

"I think it will."

Morriss stopped his pacing immediately before Lucky. His voice was a sudden bluster. "Starr, I can't believe this. The V-frogs have been in the city for years. They've been here almost since the city was built."

"You've got to remember..." began Lucky.

"That I'm under their influence?" Morriss reddened. "That isn't so. I deny it."

''There's nothing to be ashamed of, Dr. Morriss," said Lucky, crisply. "Evans was under their control for days, and Bigman and I have been controlled, too. It is possible to be honestly unaware that your mind has been continuously picked."

"There's no proof of it, but never mind," said Morriss violently. "Suppose you're right. The question is, what can we do? How do we fight them? Sending men against them will be useless. If we bring in a fleet to bombard Venus from space, they may force the dome locks open and drown every city on Venus in revenge. We could never kill every V-frog on Venus anyway. There are eight hundred million cubic miles of ocean for them to hide in, and they can multiply fast if they want to. Now your getting word to Earth was essential, I admit, but it still leaves us with many important problems."

"You're right," admitted Lucky, "but the point is, I didn't tell Earth everything. I couldn't until I was certain I knew the truth. I..."

The intercom signal flashed, and Morriss barked. "What is it?"

"Lyman Turner for his appointment, sir," was the answer.

"One second." The Venusian turned to Lucky and said in a low voice, "Are you sure we want him?"

"You had this appointment about strengthening the transite partitions within the city, didn't you?"

"Yes, but..."

"And Turner is a victim. The evidence would seem to be clear there. He is the one highly-placed official beside ourselves who would definitely seem to be one. We would want to see him, I think."

Morriss said into the intercom, "Send him up."

Turner's gaunt face and hooked nose made up a mask of inquiry as he entered. The silence in the room and the way the others stared at him would have filled even a far less sensitive man with foreboding.

He swung his computer case to the floor and said, "Is anything wrong, gentlemen?"

Slowly, carefully, Lucky gave him the bare outline of the matter.

Turner's thin lips parted. He said, weakly, "You mean, my mind...-"

"How else would the man at the lock have known the exact manner in which to keep out intruders? He was unskilled and untrained, yet he barricaded himself in with electronic perfection."

"I never thought of that. I never thought of that." Turner's voice was almost an incoherent mumble. How could I have missed it?"

"They wanted you to miss it," said Lucky.

"It makes me ashamed."

"You have company in that, Turner. Myself, Dr. Morriss, Councilman Evans..."

"Then what do we do about it?"

Lucky said, "Exactly what Dr. Morriss was asking when you arrived.' It will need all our thought. One of the reasons I suggested you be brought into this gathering is that we may require your computer."

"Oceans of Venus, I hope so," said Turner fervently.

"If I could do something to make up for..." And he

put his hand to his forehead as though half in fear that he had a strange head on his shoulders, one not his own.

He said, "Are we ourselves now?"

Evans put in, "We will be as long as we concentrate on that petroleum jelly."

"I don't get it. Why should that help?"

"It does. Never mind how for the moment," said Lucky. "I want to get on with what I was about to say when you arrived."

Bigman swung back to the wall and perched himself on the table where the aquarium once stood. He stared idly at the open jar on the other table as he listened.

Lucky said, "Are we sure the V-frogs are the real menace?"

"Why, that's your theory," said Morriss with surprise.

"Oh, they're the immediate means of controlling the minds of mankind, granted; but are they the real enemy? They're pitting their minds against the minds of Earthmen and proving formidable opponents, yet individual V-frogs seem quite unintelligent."

"How so?"

"Well, the V-frog you had in this place did not have the good sense to keep out of our minds. He broadcast his surprise at our being without mustaches. He ordered Bigman to get him peas dipped in axle grease. Was that intelligent? He gave himself away immediately."

Morriss shrugged. "Maybe not all V-frogs are intelligent."

"It goes deeper than that. We were helpless in their mental grip out on the ocean surface. Still, because I guessed certain things, I tried a jar of petroleum jelly on them, and it worked. It scattered them. Mind you, their entire campaign was at stake. They had to keep us from informing Earth concerning them. Yet they ruined everything for one jar of petroleum jelly. Again, they almost had us when we were trying to re-enter Aphrodite. The cannon was coming to an aim when the mere mention of petroleum spoiled their plans."

Turner stirred in his seat. "I understand what you mean by the petroleum now, Starr. Everyone knows the V-frogs have a craving for grease of all sorts. The craving is just too strong for them."

"Too strong for beings sufficiently intelligent to battle Earthmen? Would you abandon a vital victory, Turner, for a steak or a wedge of chocolate cake?"

"Of course I wouldn't, but that doesn't prove a V-frog wouldn't."

"It doesn't, I grant you. The V-frog mind is alien to us and we can't suppose that what works with us must work with them. Still, the matter of their being diverted by hydrocarbon is suspicious. It makes me compare V-frogs with dogs rather than with men."

"In what way?" demanded Morriss.

"Think about it," said Lucky. "A dog can be trained to do many seemingly intelligent things. A creature who had never seen or heard of a dog before, watching a seeing-eye dog guide a blind master in the days before Son-O-Taps, would have wondered whether the dog or the man was the more intelligent. But if he passed by them with a meaty bone and noted that the dog's attention was instantly diverted, he would suspect the truth."

Turner said, his pale eyes nearly bulging, "Are you trying to say that V-frogs are just the tools of human beings?"

"Doesn't that sound probable, Turner? As Dr. Mor-riss said just a while ago the V-frogs have been in the city for years, but it's only a matter of the last few months that they've been making trouble. And then the trouble started with trivialities, like a man giving away money in the streets. It is almost as though some men learned how to use the V-frogs' natural capacity for telepathy as tools with which to inflict their thoughts and orders on human minds. It is as though they had to practice at first, learn the nature and limitations of their tools, develop their control, until the time came when they could do big things. Eventually, it would be not the yeast that they were after but something more; perhaps control of the Solar Confederation, even of the entire galaxy."

"I can't believe it," said Morriss.

"Then I'll give you another piece of evidence. When we were out in the ocean, a mental voice-presumably that of a V-frog-spoke to us. It tried to force us to give it some information and then commit suicide."

"Well?"

"The voice arrived via a V-frog, but it did not originate with one. It originated with a human being."

Lou Evans sat bolt upright and stared incredulously at Lucky.

Lucky smiled. "Even Lou doesn't believe that, but it's so. The voice made use of odd concepts such as 'machines of shining metal' instead of 'ships.' We were supposed to think that V-frogs were unfamiliar with such concepts, and the voice had to stimulate our minds into imagining we heard round-about expressions that meant the same thing. But then the voice forgot itself. I remember what I heard it say. I remember it word for word: 'Life will end for your people like the quenching of a flame. It will be snuffed out and life will burn no more.'"

Morriss stolidly said again, "Well?"

"You still don't see it? How could the V-frogs use a concept like the 'quenching of a flame' or 'life will burn no more'? If the voice pretends to be that of a V-frog with no concept of such a thing as a ship, how could it have one of fire?"

They all saw it, now, but Lucky drove on furiously. "The atmosphere of Venus is nitrogen and carbon dioxide. There is no oxygen. We all know that. Nothing can burn in Venus's atmosphere. There can be no flame. In a million years no V-frog could possibly have seen a fire, and none of them can know what it is. Even granted that some might have seen fire and flame within the city domes, they could have no understanding of its nature any more than they understood our ships. As I see it, the thoughts we received originated with no V-frog, but with a man who used the V-frog only as a channel to reach from his own mind to ours."

"But how could that be done?" asked Turner.

"I don't know," said Lucky. "I wish I did. Certainly it would take a brilliant mind to find a way. A man would have to know a great deal about the workings of a nervous system and about the electrical phenomena associated with it." Lucky looked coldly at Morriss. "It might take, for instance, a man who specialized in biophysics."

And all eyes turned on the Venusian councilman, from whose round face the blood was draining until his grizzled mustache seemed scarcely visible against his pale skin.