"If he does that you can fix it again."

  "I don't think it cap be axed again, at least not in the same way with the cools we have on the boat."

  "He works like you and the Tsla or he dies now. I cannot spare the attention to let him sit and watch for a chance to surprise me."

  Etienne limped forward. "I'll watch myself, Lyra, don't worry. I can rig a sling and work with my left arm."

  "Our specimens," she muttered disconsolately. "Every­thing we've worked so hard to assemble, the first pieces of the puzzle that would enable us to start bolding a picture of this world's ecology, all thrown away."

  "They won't do us any good if we don't live to deliver them."

  "Not so stupid," Homat said approvingly. "I didn't think you were that stupid." He gestured again with the muzzle of the asynapt. "I do not like this place. Let us hurry."

  Though he worked very carefully, the pain in Etienne's side never let him alone. The internal bleeding didn't start again, but Lyra ached in her own heart as she watched him struggle to load the heavy alloy.

  Homat supervised the loading silently and displayed not a twinge of remorse. The lower hold was filled and they began stacking piles of broken metal on the second deck. Yulour carried twice his share of the toad as he toiled quietly next to his human friends.

  Several days later an exhausted Lyra, sweating inside her absorptive thermal suit, slumped to the ground and spoke sullenly to Homat.

  "That's all she'll carry."

  "No, there is yet room," Homat insisted. "Much more room. You must continue."

  "Listen to me, Homat. The sunit, the metal, is very heavy. If you stack any more on the upper decks you'll ruin the boat's stability. All the sunit in the world won't do you any good if you turn over in the middle of the Skar." She held her breath as she dropped her gaze to the ground. Actually the hydrofoil could carry another ton or so in comparative safety, but she doubted Etienne would last another day.

  Homat looked uncertain. "Very well. That is enough. Enough to buy two cities, and I can always come back for more."

  "Fine," Etienne commented. "Now let us help you deliver your damned fortune so we can go our separate ways, which won't happen soon enough for me."

  "Or if you insist on trying to take the hydrofoil back by yourself," Lyra added, "at least let us go with you as far as Tmput. We can find transportation back to Steamer Station from there, and by the time we reached our outpost you could be halfway around the Groalamasan."

  "And then what'?" Homat inquired suspiciously, his in­herent Mai paranoia surging to the fore. "Then you'll organize your friends and come looking for poor Homat with more of your strange weapons, to punish him and steal his glory." His grip on the asynapt tightened.

  Slowly Lyra got to her feet. "Homat, don't be a fool."

  "Truly that is not my intention."

  Etienne was backing toward the silent mass of alien metal. He stumbled and Lyra rushed to help him, her eyes never leaving the pistol.

  "There's no need for you to do this, Homat. We won't come after you. It's not worth it to us. It's not worth the spirit boat. We can always get another."

  "Can you?" She knew enough of Mai psychology to see that he was working himself up good and proper, trying to excite himself to the point of pushing the trigger. Killing Tyl was one thing. Mai and Tsla disliked one another and sometimes fought. But the thought of slaying them was something new. There were powerful spirits involved, strange alien spirits, and he was still unsure of himself.

  He was going to do it, though. She could see it in his eyes, read it in the way he stood, hear it in his voice. The scrawny bald little humanoid primitive was going to kill the two of them in cold blood there at the top of his world, beneath a ceiling of ancient ice, their backs to an enigma that would now never be properly studied.

  "I will keep the slave," Homat said solemnly. He gestured toward Yulour, who stood nearby looking worried and confused. "I will make use of his strength on the homeward journey. Him I do not fear, but I do not trust you. I cannot stay awake all the time to watch you. As soon as I slept you would forget all your promises, set aside your assurances, and toss poor Homat into the Skar to take his chances with the fish.

  "It is not I who is destined to be food for fishes. Not Homat the brave, Homat the great." He took aim with the heavy pistol.

  "When he settles on me," Etienne whispered as he took a step forward, "run for it. I'll take the shot and if you can get beyond the ship's lights you'll have a chance."

  "No, I won't..."

  "Don't be an idiot!" he said huskily, taking another step forward. "Now of all times." The muzzle was shifting to cover him, Homat's finger moving toward the trigger. "Use your legs, Lyra. For both of us."

  The tears were coming again, blinding her worse than the glare from the spotlights. She didn't know what to do and there was no time to make careful decisions. If only Etienne wouldn't be so damn logical! But he was right. If she could hide in the darkness of the cavern there was an outside chance she could slip aboard the hydrofoil without Homat seeing her. She was bigger and stronger than the Mai.

  Homat saw her start to back away and moved the muzzle back to cover her instead of Etienne. It was impossible to outrun the charge, but the heavy weapon was awkward in Homat's grasp. Etienne saw that he was anticipating Lyra's flight and steadied himself to leap between them to take the shot.

  He didn't have to. The same thought had occurred to someone else. Certainly no one, least of all Homat, expected Yulour to interpose himself between the pistol and its in­tended targets.

  Etienne didn't have time to wonder at the Tsla's unac­customed assertion. He was shoving at Lyra with his left hand.

  "Now, run now."

  Lyra was gaping at the Tsla. "I don't understand. Yulour doesn't act on his own."

  "Don't worry about it now, shut up and run!"

  She left him leaning on his crutch as she whirled and bolted for the blackness to their left. Homat turned to aim at her, but once more Yulour made certain his body was between hers and the gun.

  "Get out of the way, moron!" Homat shouted. Yulour stood quietly, holding his ground. "I said get out of the way! I need you for the journey Downriver."

  He could hear the gravel flying from beneath the human female's boots. Of course, he could abandon both of them, leave them to die slowly, but he was furious that his carefully rehearsed triumph might be spoiled by a simpleminded Tsla. He stared over the barrel of the lightning thrower.

  "You brought this on yourself, idiot. I'll just have to get along without you. Downriver I'll find plenty of willing backs with sensible heads atop them." He touched the trigger.

  There was a bright, crisp flash of light as the asynapt fired, accompanied by a familiar faint crackling sound. Etienne shouted, "No!" and tried to throw himself at Homat. Given the distance that still separated him from the Mai, it was a futile gesture. A sharp pain ran from his side down his left leg and he crumpled despite the support provided by his crutch.

  Dust stung his eyes as he lay staring dumbly across the gravel. Yulour had not fallen under the impact of the charge. He hadn't fallen because he was no longer there.

  But something else was.

  Chapter Seventeen

  For an instant Etienne was positive that the charge had struck him instead. That would explain the illusion. Or per­haps the silent Yulour possessed the power of old. He blinked, and the illusion remained. His side still flamed. His nose was running. It was real.

  Where Yulour had been, what Yulour had been rose four meters toward the roof of the cavern. It was slim and silvery. The coldly viscous sides twisted and flowed like the ripples that spread out from a pebble dropped in a pond. Indeed, what had been Yulour looked a lot like a tower of opaque water. Where an internal ripple reached its apex the silvery hue became suffused with other colors: gray and white, blue and purple. They spread in irregular chromatic blotches across portions of the unstable tower, fading gradually back info the sil
ver.

  Homat stood motionless, the asynapt still clutched con­vulsively in both hands. Probably he could not have dropped it had he wanted to. Suddenly all the terrors, all the childhood fears, all the old Mai stories of demons and devils and evil spirits that he had automatically absorbed as he had matured had solidified before his bulging eyes. He started to tremble and lost control of his bowels. He was trying to scream but only a thin whispery whine passed between his parted lips.

  Through his pain Etienne thought he heard Lyra shout from her hiding place back in the artifacts. She wasn't trying to maneuver behind Homat now. All she could do was stare in wonder at the tower of pulsating quicksilver that had been Yulour. Of the three who saw, it might have been that she was the most stupefied of all, for only Lyra Redowl was familiar with the folklore anti mythologies of half a hundred worlds, and thus only she knew that what stood before them in the cavern had a basis in hypothesized reality.

  It had been seen before‑or had it? No one was certain because no reputable evidence was ever presented to conclusively prove the existence of such a creature. Rumors gave it different names, of which the one that stuck was more hopefully descriptive than verifiable.

  "I'll be damned," she murmured in awe, "a Mutable."

  Etienne heard and the word sailed through his numbed brain. A Mutable. Folktales spoke of them not only on commonwealth worlds but on the worlds of the AAnn empire and the inhabited globes that turned in emptiness outside the boundaries of the principal political entities. Every space­ traversing civilization had legends of encounters with true shape‑changers, silhouette shifters, metamorphs.

  Mutables.

  But myths and fraud dissolved in the dank cavern before the glittering reality that had been Yulour the slow‑wilted Tsla. Legend or folktale or hallucination made real, whatever it was it had saved Lyra's life. Its intentions beyond that were shrouded in speculation.

  As Etienne lay there staring at the rippling silvery shape, it occurred to him that he and Lyra were likely the first lawman beings ever to see a Mutable in its natural state.

  It had protected Lyra. That was all that really mattered.

  He wondered if the body's constant movement might be an indication of some permanent instability. As he won­dered, the tower turned slightly, showing a suggestion of what might be an eye near the top. The deep gray oval swam in a sea of silver. A second might drift alongside the first, beyond his sight. It might have a half dozen hidden dupli­cates.

  Traveling like a tree on greased treads, the Mutable moved toward the hydrofoil. The motion was silent. A single pseudopod emerged from the center of the tower, formed ten­tacles that reached for the asynapt in Homat's shaking fingers. As he watched, Etienne wondered hove the creature had shaken off the effects of the burst from the pistol.

  He wasn't given the opportunity to observe the result of a second shot, because the Mai let out a single final massive shudder, then fell sideways onto the gravel. The gun fell from limp fingers.

  At this the tentacles withdrew. It mattered not to Homat, whose crumpled form lay motionless now near one of the boat's hydrofoils, knees drawn tight against the thin chest, all hint of aggression fled along with the life force. The cause of death was clear and no autopsy could have made it any clearer: Homat had died of fright, murdered where he'd stood by his own guilt and thousands of years of accumulated racial fears.

  The Mutable inclined forward over the Mai's body. Then it straightened, pivoted slowly, and moved away. Rocks and gravel were depressed where it had passed, as if a large, heavy ball had rolled across the ground where the Mutable moved.

  Despite its size the creature traveled with ease and a graceful fluidity. Lyra kept her eyes on it as she helped Etienne back to his feet and handed him his crutch. She could recall no legend of a Mutable's harming anything, but that was small comfort as she stood in that cold, dark place supporting her badly injured husband.

  Though no pupils were visible, Lyra thought the pair of large gray spots atop the silvery mass were focused on her.

  "Please do not be afraid," the Mutable said. It spoke clearly, in Yulour's familiar voice, though without that Tsla's slowness. "Yes, I am what you call a Mutable. I am the native you knew as Yulour. Please do not be alarmed." The upper portion of the tower inclined toward the hydrofoil. "I did not mean for that one to expire, but as are all his people he was a prisoner of his own private terrors. You, however, are more mature and not subject to such."

  "Don't give us too much credit just yet," Etienne found himself mumbling. "I'm scared as hell."

  "You must not be frightened." The Mutable's voice was almost painfully gentle.

  "Mutables don't exist except as rumors," Lyra mur­mured.

  "That is how we prefer to exist. It simplifies much."

  Lyra left Etienne to stand on his own and stepped for­ward, extending a hesitant hand. "I don't want to offend, but‑could I touch you'?"

  "If it is required to establish my existence in your mind."

  "It's not. I know you're here. It's just something I'd like to do."

  "Then please do so."

  She lightly pressed against the silvery flank, discovered that it felt like warm vinyl. It took an effort of will not to jerk her fingers away, not because it was too hot but because the surface was in constant motion. She stepped back, her palm tingling.

  "If you two don't mind," Etienne said, "I'm a little tired. I think I'd better sit down." It was a measure of his ex­haustion that he allowed Lyra to help without his uttering a single wisecrack.

  "You said, `it simplifies much,"' Lyra repeated. "What does it simplify?"

  "Our work. We are caretakers, we Mutables."

  "Caretakers? For whom?"

  "For the Xunca."

  Lyra frowned. "Never heard of 'em."

  "But you know of the Tar‑Aiym and of the Hur'rikku, who dominated this grouping of stars, this galaxy, until they destroyed each other in a great war."

  "Yes, I know the histories," Lyra replied. "Both races have been gone, from this portion of the galaxy, anyway, for at least a hundred millennia."

  "The Xunca predate both. They are so ancient little more than their memory remains. We are their caretakers. Whether we are an independently evolved race or machines fashioned by them, we ourselves do not know. We know only our work."

  "These Xunca lived and ruled before both the Tar‑Aiym and the Hur'rikku?"

  "They did not rule. They simply were. Their probings reached regions that can be expressed only 'ay pure math­ematics. Reached beyond this galaxy, beyond the satellite clusters of stars you call the Magellanic Clouds. They went such places."

  "You imply a technology capable of traversing an inter­galactic gap," Etienne observed. "Such technology is not possible."

  The Mutable admonished him gently. "Did not your own kind once say the same of faster‑than‑light travel, before they learned of space‑plus and null‑space? I say to you that they the Xunca did this thing.

  "This world you call Horseye and that the dominants call Tslamaina is itself a product of Xunca technology."

  "This planet is a construct?"

  "No." Thoughtfully the Mutable moved to its right so they could observe it free of the glare from the hydrofoil's lights. It was a gesture of courtesy and Etienne lot himself relax further.

  "The Xunca did not build this world, they modified it to suit their needs. The asteroidal collision which produced the oceanic basin now filled by the (Broalamasan's waters was not an astronomical accident."

  "Why do that?"

  "The Xunca required a large body of water which would circulate only in one direction, whose currents would never change. The positioning of the four small moons assures this. Here the oceanic currents flow eternally in the direction you call clockwise.

  "This perpetual motion, driven by lunar gravity, never needs refueling or maintenance. It exists and was designed to drive great engines buried in the ocean floor. Since Tsla­maina is tectonically stabl
e and has been for eons save for one regrettable massive earth tremor, there is no danger of the machinery's being destroyed by subduction. It sits and waits, ready to be driven by the mechanism of the ocean currents. The currents that scour the bottom of the Crroal­amasan are very powerful by the standards of most worlds. This construction was necessary because there are no other stable oceanic worlds in this area. The machinery is shielded against detection by space‑going peoples. It has lain dormant far tens of thousands of your years."

  "How many tens of thousands?" Lyra wondered aloud.

  "Enough to total several hundred millions."

  "And you've been `caretaking' the facilities all that time?"

  "We are long‑lived or well‑designed," the Mutable ex­plained matter‑of‑factly.

  "I don't care," Lyra argued. "Nothing lives for a hundred million years?"

  "The rocks beneath your feet do. Our internal structure resembles them more than it does yours. You may be in­terested to know that a smaller installation, similar to that which sleeps beneath the ocean of this world, exists on yours."

  Lyre started. "On Earth'? Nothing hike what you describe has ever been found. Is the shielding against detection that effective?"

  "Yes, but that installation was destroyed by your world's continental drift. It was emplaced when your continents were one large land mass and there was a single, much larger, world ocean like that on Tslamaina. The Xunca were not omnipotent. They could not plan for every eventuality.

  "But that was only a small relay and its loss not vital to the system. The main transmitter was constructed on this world. The three local intelligent life forms evolved inde­pendently long after its emplacement. They do not suspect its existence. None do." He gestured past them.

  "This is a tiny portion of the transmitter's antenna system. )Most of it lies beneath your feet. It is our task to see that it remains in operating condition, together with the extensive relay network to which it can be linked."

  "Can it operate through the ice cap?"

  "No. In the event that the transmitter system becomes active, a portion if not all of this ice will be melted."