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.
XVII 
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 into the silver.
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 and 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 sifted 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-witted 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 human 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 how 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.”
