Raf was two streets away from the circling box but still able to keep it in sight when its easy glide stopped, and, in a straight line, it swooped toward a roof emitting a shrill, rising whistle. It rose again a few seconds later as if baffled, but it continued to hover at that point, keening forth its warning. The pilot reached the next building, but a street still kept him away from the conical structure above which the box now hung.

Undecided, he stayed where he was. Should he go down to street level and investigate? Before he had quite made up his mind he saw the foremost of the alien scouting party round into the thoroughfare below and move purposefully at the cone tower, weapons to the fore. Judging by their attitude, the box had run to earth there the prey they had been searching for.

But it wasn't to be so easy. With another eerie howl the machine soared once more and bobbed completely over the cone to the street which must lie beyond it. Raf knew that he could not miss the end of the chase and started on a detour along the roof tops which should bring him to a vantage point. By the time he had made that journey he found himself on a warehouse roof which projected over the edge of the river.

From a point farther downstream a small boat was putting out. Two of the aliens paddled while a third crouched in the bow. A second party was picking its way along the bank some distance away, both groups seemingly heading toward a point a building or two to the left of the one where Raf had taken cover.

He heard the shrilling of the box, saw it bobbing along a line toward the river. But in that direction there was only a mass of green. The end to the weird chase came so suddenly that he was not prepared, and it was over before he caught a good look at the quarry. Something moved down on the river bank and in that same instant the box hurtled earthward as might a spear. It struck, and the creature who had just crawled out—out of the ground as far as Raf could see—toppled into the stream. As the waters closed over the body, the box slued around and came to rest on the bank. The party in the boat sent their small craft flying toward the spot where the crawler had sunk.

One of the paddlers abandoned his post and slipped over the side, diving into the oily water. He made two tries before he was successful and came to the surface with the other in tow. They did not try to heave the unconscious captive into the boat, merely kept the lolling head above water as they turned downstream once more and vanished from Raf's sight around the end of a pier, while the second party on the bank reclaimed the now quiet box and went off.

But Raf had seen enough to freeze him where he was for a moment. The creature which had popped out of the ground only to be struck by the box and knocked into the river—he would take oath on the fact that it was not one of the furred animals he had seen on the sea island. Surely it had been smooth-skinned, not unlike the aliens in conformation—one of their own kind they had been hunting down, a criminal or a rebel?

Puzzled, the pilot moved along from roof to roof, trying to pick up the trail of the party in the boat, but as far as he could now see, the river was bare. If they had come ashore anywhere along here, they had simply melted into the city. At last he was forced to use the homing beam, and it guided him back across the deserted metropolis to the field.

There was still activity about the globe; they were bringing in the loot from the warehouse, but Lablet and Hobart stood by the flitter. As the pilot came up to them, the captain looked up eagerly.

"What happened?"

Raf sensed that there had been some change during his absence, that Hobart was looking to him for an explanation to make clear happenings here. He told his story of the hunt and its ending, the capture of the stranger. Lablet nodded as he finished.

"That is the reason for this, you may depend upon it, Captain. One of their own people is at the bottom of it."

"Of what?" Raf wanted to ask, but Soriki did it for him.

Hobart smiled grimly. "We are all traveling back together. Take off in the early morning. For some reason they wanted us out of the globe in a hurry—practically shoved us out half an hour ago."

Though the Terrans kept a watch on the larger ship as long as the light lasted, the darkness defeated them. They did not see the prisoner being taken aboard. Yet none of them doubted that sometime during the dusky hours it had been done.

It was barely dawn when the globe took off the next day, and Raf brought the flitter up on its trail, heading westward into the sea wind. Below them the land held no signs of life. They swept over the deserted, terraced city that was the gateway to the guarded interior, flew back over the line of sea islands. Raf climbed higher, not caring to go too near the island where the aliens had wrought their terrible vengeance on the trip out. And all four of the Terrans knew relief, though they might not admit it to each other, when once more Soriki was able to establish contact with the distant spacer.

"Turn north, sir?" the pilot suggested. "I could ride her beam in from here—we don't have to follow them home." He wanted to do that so badly it was almost a compulsion to make his hand move on the controls. And when Hobart did not answer at once, he was sure that the captain would give that very order, taking them out of the company of those he had never trusted.

But Lablet spoiled that. "We have their word, Captain. That anti-grav unit that they showed us last night alone—"

So Hobart shook his head, and they meekly continued on the path set by the globe across the ocean.

As the hours passed Raf's inner uneasiness grew. For some queer reason which he could not define to himself or explain to anyone else, he was now possessed by an urgency to trail the globe which transcended and then erased his dislike of the aliens. It was as if some appeal for help was being broadcast from the other ship, drawing him on. It was then that he began to question his assumption that the prisoner was one of them.

Over and over again in his mind he tried to re-picture the capture as he had witnessed it from the building just too far away and at slightly the wrong angle for a clear view. He would swear that the body he had seen tumble into the flood had not been furred, that much he was sure of. But clothing, yes, there had been clothing. Not—his mind suddenly produced that one scrap of memory—not the bandage windings of the aliens. And hadn't the skin been fairer? Was there another race on this continent, one they had not been told about?

When they at last reached the shore of the western continent and finally the home city of the aliens, the globe headed back to its berth, not in the roof cradle from which it had arisen, but sinking into the building itself. Raf brought the flitter down on a roof as close to the main holding of the painted people as he could get. None of the aliens came near them. It seemed that they were to be ignored. Hobart paced along the flat roof, and Soriki sat in the flyer, nursing his com, intent upon the slender thread of beam which tied them to the parent ship so many miles away.

"I don't understand it." Lablet's voice arose almost plaintively. "They were so very persuasive about our accompanying them. They were eager to have us see their treasures—"

Hobart swung around. "Somehow the balance of power has changed," he observed, "in their favor. I'd give anything to know more about that prisoner of theirs. You're sure it wasn't one of the furry people?" he asked Raf, as if hoping against hope that the pilot would reply in doubt.

"Yes, sir." Raf hesitated. Should he air his suspicions, that the captive was not of the same race as his captors either? But what proof had he beyond a growing conviction that he could not substantiate?

"A rebel, a thief—" Lablet was ready to dismiss it as immaterial. "Naturally they would be upset if they were having trouble with one of their own men. But to leave now, just when we are on the verge of new discoveries—That anti-gravity unit alone is worth our whole trip! Imagine being able to return to earth with the principle of that!"

"Imagine being able to return to earth with our skins on our backs," was Soriki's whispered contribution. "If we had the sense of a Venusian water nit, we'd blast out of here so quick our tail fumes'd take off with us!"

Privately Raf concurred, but the urge to know more about the mysterious prisoner was still pricking at him, until he, contrary to his usual detachment, felt driven to discover all that he could. It was almost, but Raf shied away from that wild idea, it was almost as if he were hearing a voiceless cry for aid, as if his mind was one of Soriki's coms tuned in on an unknown wave length. He was angrily impatient with himself for that fantastic supposition. At the same time, another part of his mind, as he walked to the edge of the roof and looked out at the buildings he knew were occupied by the aliens, was busy examining the scene as if he intended to crawl about on roof tops on a second scouting expedition.

Finally the rest decided that Lablet and Hobart were to try to establish contact with the aliens once more. After they had gone, Raf opened a compartment in the flitter, the contents of which were his particular care. He squatted on his heels and surveyed the neatly stowed objects inside thoughtfully. A survival kit depended a great deal on the type of terrain in which the user was planning to survive—an aquatic world would require certain basic elements, a frozen tundra others—but there were a few items common to every emergency, and those were now at Raf's fingertips. The blast bombs, sealed into their pexilod cases, guaranteed to stop all the attackers that Terran explorers had so far met on and off worlds, a coil of rope hardly thicker than a strand of knitting yarn but of inconceivable toughness and flexibility, an aid kit with endurance drugs and pep pills which could keep a man on his feet and going long after food and water failed. He had put them all in their separate compartments.

For a long moment he hunkered there, studying the assortment. And then, almost as if some will other than his own was making a choice, he reached out. The rope curled about his waist under his tunic so tautly that its presence could not be detected without a search, blast bombs went into the sealed seam pocket on his breast, and two flat containers with their capsules were tucked away in his belt pouch. He snapped the door shut and got to his feet to discover Soriki watching him. Only for a moment was Raf disconcerted. He knew that he would not be able to explain why he must do what he was going to do. There was no reason why he should. Soriki, except for being a few years his senior, had no authority over him. He was not under the com-tech's orders.

"Another trip into the blue?"

The pilot replied to that with a nod.

"Somehow, boy, I don't think anything's going to stop you, so why waste my breath? But use your homer—and your eyes!"

Raf paused. There was an unmistakable note of friendliness in the com-tech's warning. Almost he was tempted to try and explain. But how could one make plain feelings for which there was no sensible reason? Sometimes it was better to be quiet.

"Don't dig up more than you can rebury." That warning, in the slang current when they had left Terra, was reassuring simply because it was of the earth he knew. Raf grinned. But he did not head toward the roof opening and the ramp inside the building. Instead he set a course he had learned in the other city, swinging down to the roof of the neighboring structure, intent on working away from the inhabited section of the town before he went into the streets.

Either the aliens had not set any watch on the Terrans or else all their interest was momentarily engaged elsewhere. Raf, having gone three or four blocks in the opposite direction to his goal, made his way through a silent, long-deserted building to the street without seeing any of the painted people. In his ear buzzed the comforting hum of the com, tying him with the flitter and so, in a manner, to safety.

He knew that the alien community had gathered in and around the central building they had visited. To his mind the prisoner was now either in the headquarters of the warriors, where the globe had been berthed, or had been taken to the administration building. Whether he could penetrate either stronghold was a question Raf did not yet face squarely.

But the odd something which tugged at him was as persistent as the buzz in his earphones. And an idea came. If he were obeying some strange call for assistance, couldn't that in some way lead him to what he sought? The only difficulty was that he had no way of being more receptive to the impulse than he now was. He could not use it as a compass bearing.

In the end he chose the Center as his goal, reasoning that if the prisoner were to be interviewed by the leaders of the aliens, he would be taken to those rulers, they would not go to him. From a concealed place across from the open square on which the building fronted, the pilot studied it carefully. It towered several stories above the surrounding structures, to some of which it was tied by the ways above the streets. To use one of those bridges as a means of entering the headquarters would be entirely too conspicuous.

As far as the pilot was able to judge, there was only one entrance on the ground level, the wide front door with the imposing picture-covered gates. Had he had free use of the flitter he might have tried to swing down from the hovering machine after dark. But he was sure that Captain Hobart would not welcome the suggestion.

Underground? There had been those ways in that other city, a city which, though built on a much smaller scale, was not too different in general outline from this one. The idea was worth investigation.

The doorway, which had afforded him a shelter from which to spy out the land, yielded to his push, and he went through three large rooms on the ground floor, paying no attention to the strange groups of furnishings, but seeking something else, which he had luck to find in the last room, a ramp leading down.

It was in the underground that he made his first important find. They had seen ground vehicles in the city, a few still in operation, but Raf had gathered that the fuel and extra parts for the machines were now so scarce that they were only used in emergencies. Here, however, was a means of transportation quite different, a tunnel through which ran a ribbon of belt, wide enough to accommodate three or four passengers at once. It did not move, but when Raf dared to step out upon its surface, it swung under his weight. Since it ran in the general direction of the Center he decided to use it. It trembled under his tread, but he found that he could run along it making no sound.

The tunnel was not in darkness, for square plates set in the roof gave a diffused violet light. However, not too far ahead, the light was brighter, and it came from one side, not the roof. Another station on this abandoned way? The pilot approached it with caution. If his bump of direction was not altogether off, this must be either below the Center or very close to it.

The second station proved to be a junction where more than one of the elastic paths met. Though he crouched to listen for a long moment before venturing out into that open space, he could hear or see nothing which suggested that the aliens ever came down now to these levels.

They had provided an upward ramp, and Raf climbed it, only to meet his first defeat at its top. For here was no opening to admit him to the ground floor of what he hoped was the Center. Baffled by the smooth surface over which he vainly ran his hands seeking for some clue to the door, he decided that the aliens had, for some purpose of their own, walled off the lower regions. Discouraged, he returned to the junction level. But he was not content to surrender his plans so easily. Slowly he made a circuit of the platform, examining the walls and celling. He found an air shaft, a wide opening striking up into the heart of the building above.

It was covered with a grille and it was above his reach but....

Raf measured distances and planned his effort. The mouth of a junction tunnel ran less than two feet away from that grille. The opening was outlined with a ledge, which made a complete arch from the floor. He stopped and triggered the gravity plates in his space boots. Made to give freedom of action when the ship was in free fall, they might just provide a weak suction here. And they did! He was able to climb that arch and, standing on it, work loose the grille which had been fashioned to open. Now....

The pilot flashed his hand torch up into that dark well. He had been right—and lucky! There were holds at regular intervals, something must have been serviced by workmen in here. This was going to be easy. His fingers found the first hold, and he wormed his way into the shaft.

It was not a difficult climb, for there were niches along the way where the alien mechanics who had once made repairs had either rested or done some of their work. And there were also grilles on each level which gave him at least a partial view of what lay beyond.

His guess was right; he recognized the main hall of the Center as he climbed past the grid there, heading up toward those levels where he was sure the leaders of the aliens had their private quarters. Twice he paused to look in upon conferences of the gaudily wrapped and painted civilians, but, since he could not understand what they were saying, it was a waste of time to linger.

He was some eight floors up when chance, luck, or that mysterious something which had brought him into this venture, led him to the right place at the right time. There was one of those niches, and he had just settled into it, peering out through the grid, when he saw the door at the opposite end of the room open and in marched a party of warriors with a prisoner in their midst.

Raf's eyes went wide. It was the captive he sought; he had no doubt of that. But who—what—was that prisoner?

This was no fur-covered half-animal, nor was it one of the delicate-boned, decadent, painted creatures such as those who now ringed in their captive. Though the man had been roughly handled and now reeled rather than walked, Raf thought for one wild instant that it was one of the crew from the spacer. The light hair, showing rings of curl, the tanned face which, beneath dirt and bruises, displayed a very familiar cast of features, the body hardly covered by rags of clothing—they were all so like those of his own kind that his mind at first refused to believe that this was not someone he knew. Yet as the party moved toward his hiding place he knew that he was facing a total stranger.

Stranger or no, Raf was sure that he saw a Terran. Had another ship made a landing on this planet? One of those earlier ships whose fate had been a mystery on their home world? Who—and when—and why? He huddled as close to the grid as he could get, alert to the slightest movement below as the prisoner faced his captors.