JUST BEFORE DAWN the yacht coasted to a stop outside the high stone walls of the north side of the island of Shimdoog. Green had dropped the sail and, judging his speed exactly, had steered the craft until its side was almost scraping the wall. As soon as the roller stopped, Green put Lady Luck in a bag tied to his belt and cautioned her to keep quiet. Then he began climbing up the rungs nailed to the mast. The boy followed him, and both crawled out upon the spar. Green tied one end of a long rope around the end of the spar. Then he let himself down on it to the ground on the other side of the wall.
     After the boy had also descended they paused for a moment, crouched, ready to run at the first sign they'd been seen. But there was no outcry.
     The big moon, though dropping to the horizon, was bright enough for them to make good progress. Green led the way up a series of hills, heading in a circuitous fashion toward the highest. Twice he had to step and warn Grizquetr about the towers ahead, where sentries were stationed. Lady Luck seemed to know she should be silent. Her eyes glowed and her teeth flashed, but she was only making a soundless snarl.
     They saw the fires of the guards and heard their muttered voices, but none saw them. It was doubtful that the sentinels ever did look out, for they did not think that any man in his right senses would be roaming about in the darkness, where it was well known that ghosts and demons waited for foolish mortals.
     Just before they began climbing the slope of the peak that was their goal, Green whispered. "This island is built much like the first one we encountered. I think that all of these islands are more or less similar, all being composed of a base of a mile and a half square of eternum metal or something like eternum. And all covered with rock and dirt and trees and vegetation and stocked with birds and beasts. I suppose that the original builders landscaped these craft for aesthetic reasons. After all, a sheet of metal with a few metal chambers on it doesn't look very pretty and would make a blinding glare in the sunshine."
     "Uh," replied the boy, who didn't understand.
     "Do you know, it's strange that I was right the first time when I sarcastically referred to the roaming islands as glorified lawn-mowers?"
     "What?"
     "Yes, in the beginning there must have been many more than there are now, enough to keep the vast plains looking neat and well-kept, the grass clipped, the forests prevented from encroaching well-defined limits, and so on. But when there were no longer any maintenance men to keep them going, they stopped, one by one, until at this present time there are perhaps a few hundred. Though, I don't know, there may be more. Anyway, whenever one did run down or break down for some reason or other it was soon erased by a still-functioning island."
     "Erased?"
     "Yes, for it's quite obvious to me that the islands not only cut grass, they kept the plains free of obstructions that weren't supposed to be there. And a dead island would constitute just such a hazard."
     Grizquetr spoke in a thin voice, "Perhaps, Father, I may yet understand you. I must be stupid,"
     "Far from it. You'll learn in time. Anyway, I should have known what they really were when I heard the tales of the sailors. Remember that one about the big hole made by the meteorite? And how something mysterious filled it in and covered it with turf? And then there was the way that wrecked 'rollers would vanish down to the last nut and bolt and the skeletons of the dead aboard. And there was the legend of Samdroo the Tailor Turned Sailor and what he found in the metal chambers inside an island. The great white eye through which he saw what was outside the island. And the other paraphernalia. They weren't the property of a wicked magician, as the tale would have it. Any Earthman would recognize TV and radar and dials and controls."
     "Tell me more."
     "I will when we get over this wall."
     Green had stopped before a barrier of stone, reaching at least forty feet high. A grim crown, it completely encircled the top of the hill. "Once it must have been difficult to scale, but mortar has crumbled here and there, and vines grow all the way up. Follow me. I remember exactly the path I took."
     He jumped up on a little ledge, seized a thick vine and hauled himself up to another minor projection. Unhesitatingly, the boy swarmed up after him.
     Panting, they reached the top, where they rested a moment and wiped the blood from their lacerated fingertips. The cat was the only one that seemed unperturbed. Silently, Green pointed out the twenty foot high statue of the Fish Goddess below, her back turned to them as she gestured at the cave mouth with the rocket-shaped charm.
     For the first time Grizquetr seemed scared. Like all his fellows, he had an unhealthy awe for the supernatural. This place, so walled off, so utterly ancient-looking, so invested with all the attributes of taboo, so invocative of the horrible tales of demons and angry gods, depressed him. Only his father's seeming indifference to any fiends they might encounter kept him from turning tail and backing down the wall.
     "One thing I'll bet, and that is that Miran didn't follow me this far but stayed down on the ground. With that belly of his he'd never have made it; he'd have tumbled off like a big fat bug and been squashed like one, too. Wouldn't that have been awful! However, he didn't have to go all the way with me. The very fact that I would dare to enter a taboo area is enough to condemn me, I should have slit his throat when Amra told me he'd been shadowing me. But I couldn't do it without absolutely convincing evidence, and even if I'd had that I suppose I'm too civilized to kill him in cold blood."
     "You should have told me how you felt," said Grizquetr. "I would have slipped a dagger through the tallow over his ribs."
     "No doubt, and so would your mother. Well, down we go."
     And he set the example by throwing his leg over the edge of the wall and letting himself down, somewhat gingerly. The descent was even worse than the ascent, but he didn't bother telling the boy that. By the time he found out he'd be at the bottom.
     Even so, when he reached ground, he thought that the lad couldn't be one whit more shaky than he. Forty feet was a long, long way when you were up on top looking down, especially in the moonlight.
     "This is the second time I've done it, but I don't think I'd have guts enough for a third time," said Green.
     "But we have to climb back out, don't we?"
     "Oh, we'll have to go over it, but I hope it won't be so high by then," said Green, looking mysterious.
     "What do you mean?"
     "Well I hope those stones will all be tumbled to the ground. In fact, it's a necessity, if we're to do what I expect to do."
     He took the bewildered boy by the hand and led him past the cold and silent statue and into the cave's entrance. "We could use a light," he said, "but a torch would have been too awkward to carry up that wall, and we can grope our way to the rooms that are lighted."
     Wonder why the passageway wasn't lighted, too? he thought. Or had this cave been added by the savages who used to live on the island, so that the sanctum sanctorum would have to be approached through darkness? Perhaps it was, the primitives having constructed such a chamber so that the initiate into the religion could go through darkness both literal and symbolical and come into a light that also embraced both worlds? He didn't and couldn't know; he could only guess.
     But I can take advantage of what I do have on hand, he said to himself, gritting his teeth with determination.
     The dust beneath his feet gave way to clean metal. They rounded a corner and found themselves in a chamber much like the one upon their first island, except that this had furniture. A skeleton lay in the middle of the floor, face down. The back of the skull exhibited a great hole.
     "He may have been here far a thousand years or more," said Green. "I'd like to know his story. But I never will."
     "Do you think the Goddess killed him?"
     "No, nor the demons either. It was the hand of man struck him down, my boy. If it's violent death you're trying to explain, don't drag in the supernatural. There's enough murder in the hearts of humankind to take care of every case."
     In the third room Green said, "There's no wall of dust to stop us. The ionic charges haven't stopped working. Notice how clean everything is. Ah, here we are! Before the door!"
     Grizquetr looked puzzled. "Door? I see only a blank wall."
     "That's all I saw too," said Green, "and that is all I would ever have seen, if it hadn't been for the tale of Samdroo."
     "Let me tell you how you got in!" chattered the boy excitedly. "I know what you were thinking of, what you did. You stood before the wall and you made a sign like this on it!"--He traced a rough outline of a rocket against the cool white metal--"and the wall suddenly slid to one side, and you had an entrance. See!"
     A whole section had moved noiselessly into the wall, leaving a round doorway.
     "Yes, I remembered the story of Samdroo and, though it was ridiculous to think that it would work, I did what the Sailor did. Remember that the cannibals were after him, and he ran into the cave and came to just such a blank wall. And he, wishing to protect himself against the evil spirits that he was sure lived in the cave, traced the sign that is supposed to prevent them from touching a man. And the door slid open and he plunged on into the chambers of the wicked magician, the savages bowling frustratedly after him.
     "And," continued Green, "I did just what he did, and the sign proved to be an Open, O Sesame for me."
     "A what?"
     "Never mind. The point is that the ancient maintenance men must have used just such a gesture to open the door, or else used it in conjunction with other means. And if they did, then they must also have been repair technicians for the ships that landed here. Perhaps the sign of the rocket was a secret symbol for their guild. I don't know, but it sounds reasonable."
     Ignoring the boy's flood of questions, he walked into a great room. It was more bare than he'd expected when he had found it the first time; it contained four machines or their fuel supplies, all concealed in four large square metal containers. In the center of the room was a chair and an instrument panel. The panel contained six TV windows, several oscilloscopes, and dials whose purpose he didn't know. But the controls attached to the arms of the chair seemed simple enough.
     "The only trouble," he said, "is that I don't know where the activating switch is. I tried to find it the other night and couldn't. Yet, it must be so obvious that I'll feel like a fool when I do locate it."
     Vainly he pulled at the little levers set in the arms.
     "My failure to activate this was the main reason I returned to the yacht and sailed on to Estorya. Of course, I had to go and find out just what the situation was and get a good idea of my plan of campaign. Perhaps if I'd stayed here and taken a chance on going into the city blind, we'd have been better off. At least, your mother wouldn't now be in prison, and we wouldn't have the additional worry of rescuing her."
     He rose from the chair and began pacing back and forth.
     "How ironic if I'd come this far and could get no farther! But then, what else could I expect? It's up to me to solve this, and I'm not infallible, omniscient. It should be functioning as of now. I know that the ring of rocket-shapes has got it paralyzed so it can't act. Nevertheless, unless it's blown a fuse, gone neurotic from frustration, or just worn out, there should be some indication that it is still in operation."
     "What do you mean?" said Grizquetr. "How can the island be paralyzed?"
     Green stopped pacing to gesture at the radarscopes. "See those? Well, there should be some funny lines squiggling across it, or little dots moving, or arcs sweeping across it. They would be indicating the shapes of things in the immediate neighborhood outside the island, and the lay of the land. Thus, I imagine that in the ancient days, when it spotted a rocket shape, which would then have been a genuine spaceship and not a mockup, it would have detoured around it. The whole island was, in one of its functions, a field attendant, a scavenger. It removed anything from the plain that wasn't supposed to be there. There's why they now attack 'rollers and crush them and disintegrate the parts that fall beneath their bases. That also explains why the island is trapped by a ring of rocket-shaped towers. The radar detects a complete circle and, being unable to molest any object shaped like a rocket, it squats in one place until it runs down or the rocket shapes are removed.
     "Of course, it worked automatically. But there were controls for a man to operate it when there was a special job to do or if he had to take it to another place it ordinarily wouldn't go when on automatic. These controls must be the ones.
     "The question is, does the island switch itself off and on at certain intervals, scanning the area around it to see if the inhibiting objects have gone? If so, there's no telling how long we may have to wait before its next sweep. And we just can't afford to wait!"
     He was in agony. As long as he could keep his body and brain in action, he felt he was progressing. But as soon as he had to wait upon some inanimate object that he couldn't attack, or came across a seemingly unsolvable problem, he was lost. He just didn't have the patience.
     Lady Luck whined. She was tired of being imprisoned in the bag at Green's waist and felt that she had been a good girl long enough.
     Absently, he lifted her out and put her on the table. She stretched, yawned, licked her lips, and then padded across the table. Her tail switched back and forth, and its tip brushed the surface of the centrally located TV screen.
     Immediately, a metal ball on the panel glowed red and a sharp whistle sounded. Two seconds later, light sprang into being in all of the viewers.