“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 by 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 inter-galactic 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 let 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 Groalamasan’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 stable 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 Groalamasan 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 for 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.”

Lyra started. “On Earth? Nothing like 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.”

Etienne’s thoughts moved rapidly. “That would raise the level of the Groalamasan enough to flood every major city on Tslamaina.”

The Mutable sounded apologetic. “As I have said, all this was designed a very long time ago, and the Xunca could not foresee everything. However, it is possible this will never occur. The system has not become active in all the hundreds of millions of years since it was fashioned. Who knows how many millions more will pass before anything happens? Nothing may ever happen.”

“Nobody builds something like this,” Etienne muttered, “thinking it will never be used.”

“Why not, Etienne?” Lyra said with disarming calmness. “What about the security alarms people put in their homes?” She looked startled. “Is that what this is?”

“We do not know what the system is for,” the Mutable replied sadly. “Not one of us knows. We are only caretakers, not operators or builders. We do what we were instructed to do eons ago. Watch over the system and insure that it remains intact.

“Do not think that we merely sit and wonder. We discuss and debate. We have our own culture. Now and then we assume one of the shapes of the space-going races and visit each other, for only one of us is assigned to each world. We assist one another in diagnosing and solving problems, but generally there is little to do. The Xunca built for the ages. But as to the purpose of the system, only the Xunca themselves know that.”

“What happened to them?” Etienne asked. “If they were such masters of science, why did they let the Tar-Aiym and the Hur’rikku usurp their place?”

“The Tar-Aiym and the Hur’rikku usurped nothing. Both races rose to power in the vacuum left by the departure of the Xunca. They did not force the Xunca to leave. The Xunca were never forced to do anything. They departed because they found something their technology could not cope with.”

“Then why leave this elaborate system behind? To let them know when it was safe for them to return? You must know something about it?”

“Only that it will become active if whatever it was intended to react to manifests itself.” The Mutable hesitated. “We do know that it involves one particular section of space.”

“Can you be any more specific?”

“It lies in the direction of the constellation you call Bootes, as seen from your Earth, but farther out. It is an area of modest size, some three hundred million light-years across, encompassing a volume of approximately one million cubic megaparsecs.”

Etienne frowned for a moment until the figures quoted by the Mutable linked up with something in his memory.

“The Great Emptiness. We’ve known of it for hundreds of years. It’s a ‘modest’ region, all right. It ought to be as filled with galaxies and nebulae as any other section of space, but it’s not. There’s nothing there, astronomically speaking. Some free hydrogen and a few isolated stellar masses of uncertain composition.”

“This we know,” the Mutable admitted. “What we do not know is how the Xunca transmitter is involved.”

“I’d rather it were connected to something simpler to explain,” Etienne muttered. “We humans are a gregarious bunch. We like crowds, not big emptinesses.”

“You are concerned.”

“It seems the Xunca were. Don’t you sense some kind of threat?”

“We do not worry, nor should you. Too much time has passed without anything happening.”

“Then you do think a threat of some sort is involved.”

“We have had much time in which to evaluate possibilities. When one’s entire existence is devoted to a single task, there is a fair amount of time to devote to idle speculation. I must admit that some of us believe the Xunca system to be a warning device.”

“Strange, but your words don’t give me much comfort,” Lyra muttered.

“I wish that I could allay all concerns. We wish no less for ourselves. You should know that. We have had to content ourselves with a saying: ‘the Xunca moved in mysterious ways.’”

Etienne forced himself to think of more immediate matters. All the talk of vast empty sections of space, of alien devices lying dormant for incalculable eons waiting for some unknown problem to manifest itself, of caretakers who could change their shape moving unobserved among different civilizations, was making him dizzy.

He needed to talk about something he could relate to. “Your task, then, is to ensure the inviolability of the Xunca system.”

“That is so.”

Etienne drew Lyra close to him. “Then that means you must have decided by now what you’re going to do with us.”