coordinated brains. But the mechanism controlling the asteroid's invisibility was not destroyed. The place remained invisible."

The old scientist's face grew tense. Carse paused for a moment.

"That means," he went on, "that Ku Sui provided the invisibility machine with special protection for just such an emergency. And do you think he would give it such protection and not his coordinated brains? Wouldn't he first protect the brains, his most cherished possession?"

Eliot Leithgow knew what this meant. The Hawk had promised the brains in that machine—brains of five renowned scientists, kept cruelly, unnaturally alive by Dr. Ku—that he would destroy them. And his promises were always kept.

There was no evading the logic of this reasoning. The Master Scientist nodded. "Yes," he answered. "He certainly would."

"I couldn't damage the case they were in," Carse continued. "The whole device seemed self-contained. It means just one thing: special protection. Since the mechanism for invisibility survived the crashing of the dome, we may be sure that the brain machine did too. And more than that: we may assume that there was special protection for the most precious thing of all to Dr. Ku Sui—his own life."

Friday's mouth gaped open. The old scientist cried out:

"My God! Ku Sui—still alive?"

"It would seem so," said Hawk Carse.

He amplified his evidence. "Look at these space-suits we're wearing. We got them and escaped by them, but they're Dr. Ku's. Couldn't he have protected himself with one too? He had plenty of time. And then the construction of the asteroid's buildings—all metal, with tight, sealed doors! Oh, stupid, stupid! Why didn't I see it all before? Here, in my weakness and sickness, I thought we'd killed Ku Sui and destroyed the coordinated brains!"

Leithgow looked suddenly very old and tired. The calamity did not end there. There were other angles, and an immediate one of high danger. In a lifeless voice he said:

"Carse, our whole situation's changed by this. We intended to go straight to my laboratory, but we may not be able to. The laboratory may already be closed to us. And even if not, there'd be a big risk in going there."

"Closed to us by what?" the Hawk demanded sharply. "At risk from what?"

Old Leithgow pressed his hands over his face. "Let me think a moment," he said.

There were very good reasons why Eliot Leithgow maintained his chief laboratory on the dangerous Satellite III. Other planets might have offered more friendly locations, but III possessed stores of accessible minerals valuable to the scientist's varied work, and its position in the solar system was most convenient, being roughly halfway between Earth and the outermost frontiers. Leithgow had counterbalanced the inherent peril of the laboratory's location by ingenious camouflage, intricate defenses and hidden underground entrances; had, indeed, hidden it so well that none of the scavengers and brigands and more personal enemies who infested Port o' Porno remotely suspected that his headquarters was on the satellite at all. Ships, men, could pass over it a score of times with never an inkling that it lay below.

After a short silence, Eliot Leithgow began his explanation.

"You'll remember," he told the intent Hawk, "that Ku Sui's men kidnapped me from our friend Kurgo's house in Porno. There were five of them: robot-coolies. They took us entirely by surprise, and killed Kurgo and bore me to Ku Sui's asteroid.

"Well, I had come to Kurgo's house in the first place to arrange for supplies for building an addition to my laboratory, and I had with me a sheaf of papers containing plans for this addition. The plans are not important; they tell nothing—but there was a figure on one of the papers that might reveal everything! The figure 5,576.34. Do you know what that stands for?"

The adventurer thought for a moment, then shook his head. Leithgow nodded. He went on:

"Few would. But among the few would be Ku Sui!

"You'll remember that on building my laboratory we considered it extremely important to have it on the other side of the globe from Port o' Porno—diametrically opposite—so that the movements of our ships to and from it would be hidden from that pirate port. Diametrically opposite—remember? Well, the diameter of Satellite III is 3,550 miles. This diameter multiplied by 3.1416 gives 11,152.63 miles as the circumference, and one half the circumference is 5,576.34 miles—the exact distance of my laboratory from Port o' Porno!"

"I see," Carse murmured. "I see."

"That figure meant nothing to you, nor would it to the average person; but to a mathematician and astronomer—to Dr. Ku Sui—it would be a challenge! He would be studying the paper on which it is written down. One of Eliot Leithgow's papers. Plans for an addition to a laboratory. Therefore, Eliot Leithgow's laboratory. And then the figure: half the circumference of Satellite III. Why, he would at once deduce that it gave the precise location of my laboratory!"

The Hawk rose quickly. "If those papers fell into Dr. Ku's hands—"

"He would know exactly where the laboratory is," Leithgow finished. "He would search. Its camouflage would not hold him long. And that would be the end of my laboratory—and us too, if we were caught inside."

"Yes," snapped the Hawk. "You imply that the papers were left in Kurgo's house?"

"I had them in the bottom drawer of the clothes-chest in the room I always use. The coolies did not take them. At that time they wanted nothing but me."

Friday, rubbing his woolly crown, interjected: "But, even if Ku Sui's still alive, he wouldn't know about them papers. Far's I can see, they're safe."

"No!" Leithgow cried. "That's it! They're not! Follow it logically, point by point. Assuming that Dr. Ku's alive, he has one point of contact with us—Kurgo's house, in Porno, where I was kidnapped. He wants us badly. He will anticipate that one of us will go back to that house: to care for Kurgo's body, to get my belongings—for several reasons. So he will radio down—he probably can't come himself—for henchmen to station themselves at the house and to ransack it thoroughly for anything pertaining to me. The papers would fall into their hands!"

"All right," said Carse levelly. "We must get those papers. They will either be still in the house or in the possession of Dr. Ku's men at Porno. But whichever it is—we must get them before Ku Sui does." He paused.

"Well," he said, "that means me." He turned and looked down at the old man and smiled. "There's no use risking the three of us. I'll go to Kurgo's house myself."

"If the papers are gone, suh?" asked Friday.

"I don't know. What I do will depend on what I discover there."

"But," said Leithgow, "there may be guards! There may be an ambush!"

"I have a powerful weapon. M. S. Unknown, so far; new to Satellite III. Ku Sui himself supplied it. This space-suit."

The Hawk scanned the "western" sky and began giving brisk orders.

"Eliot, you've got to go to some place of safety until this is all over. You too, Eclipse, to take care of him. Let me see.... There's Cairnes, and Wilson.... Wilson's the one. He should be at his ranch now. You remember it: Ban Wilson's ranch, on the Great Briney Lake? Right. Both of you will go there and wait. I'll meet you there when I'm finished. And at that time I'll either have the papers or know that Ku Sui has found the laboratory."

Again on his feet, the old Master Scientist regarded anxiously this slender, coldly calculating man who was his closest friend. He was afraid. "Carse," he said, "you're going back alone into probable danger. The papers—the laboratory—they're important—but not so important as your life."

There was visible now in the Hawk's face that hard, unflinching will-to-do that had