Enigma

By Sean McMullen

* * * *

Enigma hung beneath us like a mighty display screen in space, alive with colors, yet showing no picture that we could understand. There were no seas, mountains, or polar caps; neither were there clouds or forests. There was, however, a city. The entire planetary surface was a vast, empty, incomprehensible city. It was a city that could not be lived in, our robotic probes had told us that. All its surfaces were curves, arches, light wells, and tunnels. There were no roads or walkways, the mighty halls had no f loors that could be walked on, the towers were hollow, and there were no rooms, offices, balconies, windows, or steps. Because the material of the city absorbed radio-frequency signals, our probes had been lost when they went deeper than one mile into the caverns and tunnels.

The actual planet was a mass of contradictions too. Its atmosphere contained oxygen, the Hawking telescope told us that within hours of the original discovery. The presence of oxygen seemed a guarantee of life. Pure oxygen reacts with most elements, so it cannot last long without plants to renew it. Because of that, there was never any doubt that Enigma harbored life. Then came the unthinkable discovery. Spectrometers found that Enigma’s atmosphere had no water or carbon dioxide, which are also part of the life cycle as we understand it. An atmosphere of oxygen, but no life! This was beyond comprehension.

There was no radio noise, yet edge-of-resolution interferometry showed a surface texture like vast expanses of buildings. Buildings and pure oxygen indicated a highly advanced civilization, one that had progressed beyond electronics and had outgrown industrial pollution. Obviously we had merely misunderstood alien life processes. That gave the Earth hope. Enigma’s people would show us how to manage our world, they would have all the answers we needed. Now we had arrived there, but the mysteries kept piling up and we had not a single answer.

Andrean was slightly wolf, and was commander of the lander Cumulus. Five of us would share a space no bigger than a small apartment until we died, but that was no problem. We would not live long.

I was a woman who was somewhat rat. The other three had traces of terrier in their DNA. An alpha wolf, an ultraloyal pack, and an outsider—me. Someone’s computer model had once concluded that it was the near-perfect exploration team.

“Too soon, our turn,” Andrean said as we waited for the launch window.

There was a certain quality of gloom in his voice. It told me that he did not like taking chances, and that was reassuring.

“You don’t sound happy,” I prompted.

“Clever Kerris Rat. This star’s planetary system has no precedent. That worries me.”

“Why? Nine other systems have two gas giants and a single rocky planet.”

We had been engineered to disagree without actually coming to blows because that was the current theory of team dynamics. We were also just a little repelled by each other sexually, which simplified interpersonal relations.

“For anyone frightened of meteor impact, Enigma is really configured to last,” Andrean replied.

“Configured? Who could configure an entire system?”

“Who indeed, but the evidence suggests it. Here the gas giants have no moons or rings, and there are no asteroids, comets, or even meteors. Dust is at the levels of interstellar space. Enigma’s orbit even leaves it untouched when the star eventually swells into a red giant.”

I knew all of that, but it did not worry me. Wolf paranoia is different from rat paranoia because rats live their lives in danger. Rats have dwelt in the shadows of a more advanced species ever since humans evolved, but wolves live separately, in wilderness.

All six thousand planetary systems examined by the Hawking Telescope had detectable Oort clouds. Enigma’s system was the sole exception. The star’s galactic orbit took it nowhere near any other star’s Oort cloud for a hundred million years, and possibly longer.

The lander detached from the Turing with a slight lurch and began its long, long fall to the outer atmosphere.

“Okay, the system has been swept clean,” I said. “So what? We humans have done that with threatening asteroids in our own system.”

“Enigma’s system has been swept clean out to a distance of two light-years, Kerris Rat. Think about it. Pi times a radius of two lightyears cubed is over twenty-five cubic lightyears. What sort of power can do that? Just getting the Turing to Enigma pushed Earth’s orbital fabricators to the edge of capacity for three decades.”

“You seem to be driving at something.”

“I have fears, Kerris Rat. After going to so much effort to save Enigma from impact damage, don’t you think the builders might have left defenses to protect it from aliens like us? Landing the Cumulus on Enigma might be like a fly landing on the Mona Lisa.”

Andrean had a gift for unsettling imagery. I shivered.

“Our probes were not destroyed,” I said, as hopeful as a rat slinking past a sleeping cat on a cushion. “Besides, a curator would not squash a fly against a valuable artwork.”

“Only if it behaves.”

“So we must behave.”

“Behave? Relative to what rules?”

In a sense we were safe, because the expedition had been planned as a type of suicide mission. The Turing would reach Enigma, but without enough fuel to return to Earth. The Cumulus and Nimbus would descend to the surface, but could not return to orbit. When our work was done we would all suicide, but that was fine. Echo technology would bring us home.

We were attached to our echoes by streams of brain telemetry carrying our memories, sensations, and experiences. Our echoes lived in suspension tanks. To return to Earth, all that we had to do was die. Our clones would be revived once the telemetry ceased, and those clones would be us.

So were I to die, my clone would be revived, and I would be my clone. I would wake with some alarming memories of dying, but I would be alive. Were my signal to be lost, I would be considered dead, and my clone would also be revived. If all signals from the Turing ceased, Earth would assume a catastrophe and revive all of our clones at once. As a strategy it had its flaws, but it was still easier than returning our physical selves to Earth.

There had been years of legal wrangling about both our status and even the morality of constructing our echoes, yet when the time came for the Turing to leave, we originals were aboard. This was largely because the whole idea of being “human” was slipping away. Cyberlibs were campaigning for android-human marriage, lattice-heads had more RAM than synapses, and the poochers were having themselves genetically morphed to have recreational sex with their pets. Throw a stone into a crowd on Earth and your chances of hitting a template human were not good and getting worse.

Thoughts of being blotted out by some gargantuan fly swatter were with me as the Cumulus entered the outer atmosphere of Enigma. In preparation for this moment Risc Hound had piloted dozens of descents to the surfaces of Venus, Mars, Titan, and of course, Earth. Compared to all that, Enigma’s atmosphere presented him with no real challenges. After tracing a line of fire through the cloudless oxygen, the Cumulus slowed to subsonic speeds by twelve thousand feet, deployed its huge parasail, then inflated it with hydrogen. Three hours after entering the atmosphere, we were hanging a hundred feet above the spires, funnels, tubes, towers, and galleries of the city.

Although we were all wearing environment suits, these did not stop the sounds of the surface from reaching our ears and resonating through our bodies. The probes dropped by the Turing had already transmitted the symphony produced by the gentle winds of Enigma blowing through the city, but probes’ microphones did not give anything like the full effect of being down there. All the rat heritage in me shrieked for caution, yet I was just a little allured. Every tunnel, air vent, and light well, every functionless yet exquisite tube and hollow tower in the structure of Enigma’s city contributed to the sounds that caressed us.

“The music must be a lure,” said Merek Hound, the security officer.

His voice was relaxed yet halting, as if he were fighting his better judgment.

My body was shivering with the chords reverberating through it, yet I did not seem to be quite as entranced as the others. Apparently a few rat genes made a subtle but effective difference.

“Lure or not, we cannot return to orbit,” said Andrean.

“Our probes found no evidence of life or power sources,” said Elsk Hound.

“Then I judge Enigma to be safe,” concluded Merek.

This gave me no comfort. Merek was a dog chimera, and dogs can be bribed by a burglar with a slice of chicken pie. A rat would just bite his finger and run.

“Captain Leonne, will you give an opinion, over?” Andrean asked into his mouthpiece.

Leonne was back on the Turing, and thus likely to be impartial.

“There may be dangers that we can’t begin to imagine,” she said slowly, “but we can see none. Dr. Becter reports that the biosensors on your body and brain echo monitors display a state of tranquility. This may have been induced by the city’s sounds. Over.”

“So they could be a lure, over?” asked Andrean.

“They could also be a welcome, over,” said Leonne.

I looked out over the landscape of ludicrous, nonfunctional architecture that was producing the eternal music. There was no obvious threat, but that could mean anything.

“I can see no threat,” said Andrean, “but who am I to decide? From now on we shall have to rely on Kerris Rat to sense any danger.”

The caution of rats is in every cell of my body, even though I am human. The very specifically chosen rat DNA spliced into mine made me a highly effective but very cautious explorer. Uncounted millennia of sharing caves, houses, ships, and palaces with humans had taught rats to treat everything new and strange as a possible snare or trap. Unless forced to, I would not explore. Thus Andrean forced and the Hounds backed us both. There was strength in our diversity.

One never really got used to the sounds of Enigma, but it was possible to push them into the background of one’s thoughts. I could not avoid the feeling that I was like a rat in some gallery of wonderful artworks, surrounded by beauty, yet forced by my limitations to ignore what was on the walls while hunting for garbage bins to raid.

Across the entire surface of the planet there was just a single anomaly, and that was our first objective. A probe had identified it as wreckage, and from a technology not entirely different from our own. It was a mechanical arm, and it was grasping the top of a spire with its cluster of metal fingers. The other end trailed cables and torn metal, as if whatever it had been attached to had been ripped away. Long exposure to the pure oxygen and sunlight had not yet eaten into its structure, but there would come a time when it would crumble and vanish into the huge funnel at the base of the tower. How far would it fall, and to where? I did not want to think about that.

We sighted Becter’s probe standing sentinel in the distance and steered for it. It was rather like a small airship trailing six tentacle manipulators, each a hundred feet long. One of those was anchoring the probe to the spire. We approached slowly, then circled several times. The spire was one of fourteen at the edge of a field of tubes shaped like immense, inverted saxophones. At a command from Becter, back on the Turing, the probe released the spire and departed to continue its survey. With the solar-powered impellers of the Cumulus holding us steady, Andrean was lowered from the belly hatch on a cable.

“No sign of threat, over,” he reported.

“Mind your first step, over,” said Merek.

“There is nowhere to step, but I will be careful. Over.”

Only inches above the spire, Andrean hesitated.

“Commander, is there a problem, over?” asked Merek.

“Just being cautious, over.”

Andrean’s boot touched the spire’s tip.

“The surface is stable, over,” he announced.

These were not the most inspiring or auspicious words that someone could have uttered when first stepping upon an alien world. Seventeen years in the future many people on Earth would be disappointed with him, but what did that matter to a wolf? He attached himself to the spire by a loop of cable, then with exaggerated caution, descended to the mechanical arm.

“The probe identified the arm’s material as a titanium alloy,” I reminded Andrean. “Very hard, lightweight, and almost inert. Over.”

“I see corrosion, especially on the joints. Assessment, Kerris Rat? Over.”

This was all leadership and protocols. Andrean was the alpha wolf, so he had to prove his credentials by being first to go down and face the unknown. I was better qualified to investigate, but I had to be second.

“We do not know what mechanism maintains the arm’s grip on the spire,” I pointed out. “If it slips loose it will vanish into the funnel below and be lost. I suggest that you use your personal tether to secure it to the spire, then return to the Cumulus. I will then winch down to do more detailed scans and tests. Over.”

“Suggestion good. Over.”

I descended to the scrap of wreckage with a field analysis kit and utility platform. With the platform attached to the spire, I had a firm and safe footing. I began my tests.

“I can confirm the probe’s analysis: The arm’s age is 5.7 million years, over,” I reported presently.

“Humans could still interbreed with chimps when it was new,” said Andrean. “How is the structural integrity? Over.”

“Surprisingly good. I suggest on-site analysis, then winch it into the Cumulus for detailed work. I will need to work into the night for what I have to do. Over.”

“Suggestion good. Over.”

Andrean now decided to survey the immediate area from the Cumulus and promised to return the following day. I was left to study the artefact alone.

At first I took microsamples from the arm. Scraps of metal tubing, wires, cables, fibers, and even corrosion went into my snap-top phials. An ultrasonic scan gave me a good idea of its internal structure. Each joint had its own linear motor, each digit on the hand had a tiny camera above the fingertip, and there were eleven control processors. There were four fingers and two thumbs, each cushioned by layers of carbon lattice. Very hard at the molecular level, yet soft to the touch.

I ran my gloved hand along the surface of the spire. It was covered in fine oxide, and was as slick to the touch as wet ice. I rubbed off a sample of the oxide, then returned my attention to the arm. Somehow I felt strangely guilty.

All around me the city played its music, oblivious to the fact that it now had an audience. The motion of the wind through the buildings of Enigma played a strangely tranquilizing symphony that was not music, yet not random either. Chords boomed, lingered, then faded, trills rippled out in the distance, and sometimes a background like the drones of bagpipes resonated until the winds shifted again.

The sky was deep blue, due to the way oxygen polarizes sunlight. Heat shimmers made the light reflected from the varied oxides on distant buildings dance and sparkle. The colors and patterns of the buildings seemed to teeter on the edge of making sense, but they never quite did so for me. I was intrigued, but not captivated. Rats are not easily impressed.

The site was forty degrees south of Enigma’s equator, and I had been left there six hours before sunset. The plan was that I should overnight there, alone. Should anything nocturnal live on Enigma, I might be the first to see it. Or be eaten. Still, death held no terrors for me because I had an echo, on Earth, seventeen light-years away.

I extended the platform until I had two meters of space to lie down on for the night. The wind regime changed at sunset, and I discovered that the spires produced their own music. They resonated, combining individual notes into chords, yet they were not entirely pleasing to the ear. I soon realized that the ancient robotic arm plus my utility platform were acting as dampers on my base spire, spoiling its contribution to the overall effect. I was the fly on the Mona Lisa, and that gave me a little spasm of dread. Still, the robotic arm had clung there undisturbed for nearly six million years, so perhaps my fears were groundless.

Sunset was a very strange inversion of what I was used to on Earth. The buildings lit up, sparkled, glowed, flashed, morphed color, and sang their symphonies, but the sky merely faded from blue into starlit black, with a band of gold along the horizon. Beyond dusk, the darkness on Enigma was more profound than was possible anywhere on Earth. Amid the stars was the Turing, a point of light on the celestial equator, never moving.

Rat caution counseled me against turning on any lights. Countless caverns gaped open on the surface. What might emerge from them? We had detected no power sources below, yet Enigma had power available. Solar radiation drove the wind regimes, and the winds generated sounds, vibrations and who could guess what else? Tidal forces from the star’s gravity flexed the planet and might well have driven engines by compression and expansion. Sunlight falling on the surface was reflected as colors and patterns, but could also be accumulated as electrical energy. Power was definitely available for defenses.

I switched my goggles to starlight enhancement and looked around. Immediately I saw scrape marks in the mouth of the funnel below me. This was an important discovery. Enigma was designed to be viewed at its best by day, but at night one could see occasional evidence of wear. Something the size of an old-style automobile had fallen into the funnel nearly six million years ago. Time and oxidization had blurred the scrape marks, but in starlight the scoring stood out. Something had clung to the spire until the arm had ripped away, then it had fallen into the funnel.

I waited for some grisly end at the taloned hands of the unknown. It did not come. The winds played night music in Enigma’s tubes, spires, and galleries. Three hours into the fifteen-hour night I decided that I would try to sleep. The combination of mesh stretcher and environment suit was more comfortable than it sounds, and in spite of my forebodings, I eventually slept.

At the very least I had expected dreams of terrifying wonders, nightmare visions full of things incomprehensible yet horrific. I had expected to wake screaming. Instead, I awoke after a long and pleasant sleep, an hour before dawn. I had not been eaten. The gas giants Mega and Giga had risen, and steady among the moving stars was the dot of light that was the Turing. Glancing about with the starlight enhancement goggles, I quickly reassured myself that nothing had been disturbed. The intrusion monitor reported nothing either. No nocturnal visitors had called past to inspect me, molest me, or even have a taste.

Then I saw it, on the surface of a neighboring spire. It was a circle that was just slightly darker than the background oxide in the enhanced starlight. I brought my equipment to bear on it at once. It was a shallow pit, but that was as much as I could make out at distance.

After hearing of my discovery Andrean began the return trip just as fast as the impellers would move the Cumulus, and was hovering above me just two hours after dawn. First we gently detached the ancient robotic arm from the spire and winched it into the lander, then Merek and Andrean attached another platform to the neighboring spire. The scans and tests on the little pit went on until after the planet’s noon. When no more could be learned, we were all winched back into the Cumulus.

Some hours of frantic analysis followed. I examined the arm, while the others worked on scanning and interpreting the flaw in Enigma’s otherwise perfect surface. I discovered a dozen hermetically sealed pipes, and from these I extracted air samples and spores. There was also some script etched into the metal structure.

“The pit is apparently an ancient weapons strike,” Merek announced at a meeting late in the afternoon. “Some type of high-energy beam was fired from near where we found the arm.”

“Kerris Rat?” asked Andrean.

“I agree with Merek Hound.”

“Risc Hound?”

“We are left with the question of why the shot was fired,” he said, stating the absolutely obvious.

“I disagree,” I interjected.

Andrean Wolf and the three Hounds turned to me.

“Explain,” said Andrean.

“We should be asking why the probe was there, grasping the spire.”

“Well, do you have the answer?” asked Elsk Hound.

I projected several images of the spire in the area where the arm had been attached.

“See here, this oval is where I rubbed some oxide away for analysis. Now look at this, a circle of very slightly paler material, two feet farther down. This circle is why the ancient aliens were docked at the spire.”

That ended the meeting almost instantly. Within minutes we had adjourned down to the spire, but it took the rest of the afternoon to deduce what the pale patch might be. The material was a good mimic of Enigma’s surface, but it was not original. Before long we had made another discovery. There was a structure sealed beneath the circle. It was a type of data lattice. The pit below all this seemed to have been a strike from an interstellar meteorite.

Something had repaired the damage and had embedded a time capsule in the packing material. The robotic arm was 5.7 million years old, but the repair job had been done fourteen million years ago. The impact was another three million years older. A molecular scanner was left attached to the spire, reading the data arrays of what seemed to be the time capsule. I returned to examining the mechanical arm.

Late that night our meeting was reconvened.

“The arm’s chambers contain non-local air,” I reported. “Composition: 18 percent oxygen, 11 percent argon, 69 percent nitrogen, and 2 percent carbon dioxide and trace gases. To me the technology looks to be roughly parallel to that of Earth’s, but highly refined.”

“I don’t follow. It should be either inferior or ahead of us,” snapped Elsk Hound, who seemed to resent me for also being female.

“They seemed to take longer to do what humans did, and to refine everything to a greater degree, but overall, they were ahead of us. The linear motors rely on energy exchange parameters that are not possible, according to the websites where I learned physics, yet I actually got them to work.”

“So their technology is superior but comprehensible,” said Andrean.

“Yes.”

“And they were examining the time capsule left by the earlier visitors?”

“Almost certainly.”

“Very good. Continue your work. Merek Hound, what have you learned from the lattice capsule?”

“The information is in a quantum five-state convention and is structurally different from the script found on the robotic arm. We are definitely dealing with two species and cultures. So far I have identified a representation of this solar system in the data, and I am using that as a key to open up the remaining files.”

“Elsk Hound, you are working on a tissue sample, you said?”

“Yes, Andrean Wolf.”

“Explain.”

“I am running a gestation simulation from a few skin cells that Kerris Rat found in the robotic arm.”

“I thought it would have been assembled under sterile conditions,” said Andrean.

“Probably, but I think someone did field repairs to it, and in circumstances that were not quite clean-room standard. So far the unrefined DNA-analogue has provided an adult image that looks like this.”

The holo-projector conjured something in the middle of the table that combined the very worst features of a cat and a dragon. Elsk made the projection glare at me and growl. I tumbled from my seat and was backing away across the floor before I managed to fight down my fears. The Hounds were very amused. Andrean just looked slightly annoyed, as if distracted from the serious business of worrying.

The creature was apparently capable of rearing nine feet tall, and had four fingers and two opposable thumbs. The brain was structurally unlike that of a human, but of a similar capacity by volume.

“Our first look at an intelligent alien,” said Elsk.

“Its fangs mark it as a predator,” said Merek.

“I’d say its ancestors had been stalking their prey in supermarkets for centuries by the time they found Enigma,” was my opinion.

“I can’t believe this thing’s species was civilized,” said Risc.

“I can,” I said. “Two thumbs, retractable talons, and all the digits are finely formed and gracile. It was a tool maker, just as we are.”

“But the skull is long and narrow. It should be optimized and hemispherical, like ours.”

“You’re thinking like a human, Risc Hound. Birds’ brains are nothing like ours, yet crows score about as well as chimps as tool makers and users.”

Andrean now reluctantly declared that Enigma was free of hazards, so the Nimbus was sent down from orbit to help with the research. Its crew was also one of chimeras, but the composition was a little different. Silzan Hawk commanded three Hounds, and Rel Fox was the science vector. We sent the first samples up to the Turing on a small sample ascent rocket, and included some of the oxide from Enigma’s surface.

Over the days that followed a scanning survey for surface texture anomalies located dozens, then hundreds of repair sites. Most were damage from interstellar meteorites, and a third contained time capsules that we could scan. The rest seemed to have been repaired for the sake of keeping Enigma looking complete and pristine.

Back on the Turing, Becter and his people analyzed our findings, drew no sensible conclusions, then sent us in search of yet more data. From equator to poles, Enigma was covered in buildings. The style was not uniform, but the individual structures blended into each other seamlessly and each style framed the next without clashing. Backscatter-radiation sounding indicated that the material of the city was some type of silicon ceramic, highly resistant to corrosion yet slightly rubbery. Its composition varied slightly from place to place, causing the differences in surface color.

All planets shrink slowly and Enigma was no exception, but the city was designed so that no part would fracture within the estimated remaining age of the Universe. There was no rain or sand on the wind, so there was no weathering of the surface. The ceramic did react with oxygen, but only to form a thin, protective layer against further corrosion. We discovered that trace oxides in the air seemed to disrupt microbial structures at the molecular level. It was a self-sterilizing planet; even bacteria could not colonize Enigma.

The oxidation was also a dry lubricant. Everything dropped onto Enigma’s surface slid down until it reached one of the many yawning funnels and was lost to sight. This was garbage disposal on a planetary scale; the builders had really thought of everything to keep it perfect.

All of this was fascinating, but it told us nothing!

Our practical, usable discoveries were made from the mechanical arm and the time capsules dotted about on the surface. That made sense. Give a hunter from a Stone-Age tribe the choice between a good titanium alloy knife and an orbital battle platform, and he will take the knife every time. What is comprehensible is always preferable. The technology of the other alien visitors was on a par with our own, in a time period between roughly decades and millennia. On the other hand, those who had built Enigma were well beyond description, imagination, and comprehension.

Using the data files from one of the time capsules, Becter built a simulation of a planetary system that had been explored by the visitors. Included were images of what were probably ruins, shattered crystals from some type of nanotech community intelligence. They came from a water world sheathed in ice and orbiting a gas giant. The system had no star, it was just a gas giant and its moons, adrift in interstellar space. Tidal effects provided heat to maintain a layer of liquid water on two of the moons. The intelligences resided in relays arranged in crystal lattices, and these were interfaced in larger or smaller clusters depending on what sort of processing was required for a problem. They were almost unimaginably alien, but at least comprehensible. Enigma’s builders were not. Enigma had been only the second system where the visitors’ race had discovered ruins . . . if Enigma could be described as ruins.

“Andrean Wolf, I want you to look at some images,” I said. “First, the fourteen-million-year-old repair to the meteorite strike.”

“I know it well, Kerris Rat.”

“Next, the little crater left by the shot fired 5.7 million years ago.”

“No, this is one of the repaired craters.”

“I’m afraid it is the right one.”

“But it has been repaired.”

“Correct. Between today and the day we arrived, it has been repaired. I checked the activity logs. Nobody has entered the work as a job. I revisited the site. The material used for the job was aceramic used for lightweight repairs in our field maintenance kits, and it was colored to blend in with the spire.”

“Who would have done this, Kerris Rat?”

“One of us.”

“But why?”

“Because Enigma has ways of maintaining itself, Andrean Wolf.”

While the Hounds surveyed Enigma, I mapped, scanned, disassembled, refurbished, and powered up the robotic arm. Reverse engineering the thing turned out to be relatively straightforward, as the alien processors were based on layered crystal neural electronics. The power buffers for the linear motors were drained but viable, and electricity is always electricity. After some blind experimentation I charged it up, then developed some methods of control and slowly worked out the interfaces for the nodal processors.

“They were deliberately kept simple, presumably to make repairs in the field more easy,” I explained to Andrean. “Allow me to demonstrate.”

As he watched, I powered up the cameras in the fingertips. Very slowly, I used my laboratory computer system to point the unit at Andrean. An image of his face appeared as a hologram above the bench.

“And this is all being done by the alien artifact?”

“Yes. Note how the six cameras allow a three-dimensional representation. Now observe the high degree of motor control.”

With the speed of a striking snake I lunged the robotic hand at Andrean’s wrist and seized it firmly. He yelped and pulled away, beating at the mechanical fingers. I released him.

“Observe also how durable the technology is, even after millions of years in sunlight and oxygen,” I pointed out.

“Yes, I had noticed,” he said, rubbing his wrist and scowling. “Kerris Rat, I have been thinking about the images you showed me nine days ago. The repairs to the little crater.”

“Yes, yes. Do you know who did it yet?”

“All hounds deny it, as does the crew of the Nimbus. I went back over the work schedules. Look here.” He projected collection schedules onto the screen. “It had been my intention to collect samples of the many hundreds of variations of oxide that gave Enigma its patina of colors.”

“I don’t see anything unusual.”

“Look again. Really concentrate.”

I made a real effort this time, aware that he was driving at something.

“There are three hundred requests,” he said presently. “How many samples have been collected?”

“I . . . I see . . . one acknowledgment. It’s . . . early in the program.”

“Look again. How many Enigma days?”

“Three, five, two, seven . . . and the only sample taken was by me on the day we arrived!”

“Now you see it,” he concluded. “The requests are assigned to Merek, Risc, and even yourself. It gets better. I scheduled you to take samples of the underlying material of several sites in the city. How many have you drilled out?”

“None,” I managed, after some concentration.

“Yes indeed, none. Kerris Rat, Enigma is protecting itself. It has messages in the windsongs, subsonics and visual patterns. The city seems to have a way of compelling visitors like us to do no damage and to help with its upkeep.”

“But I feel no urge to rush out and repair things.”

“Were you to find some damage, I think you would have a change of heart.”

“This . . . ought to feel alarming,” I conceded.

“Once again, Enigma at work. Becter asked for some laser ionization sampling to be done fifteen days ago. Not only did you forget about it, but he did too. I remembered. Strength in diversity.”

“Becter forgot? Becter is in orbit. How could he be influenced?”

“From orbit he can see Enigma’s surface. Even viewed from space, the changing light on the surface seemed to generate subliminal effects on some brains. It’s . . . taking control of us, no matter where we are.”

“So Enigma was designed to inf luence us, but how?” I wondered, “We were blobs of jelly in some Pre-Cambrian sea when it was built.”

“All true, Kerris Rat.”

“How?”

“I do not know, but we are definitely changing. All of our experiences are being streamed back to Earth. That means our echoes are changing too. The—the infection may already be back on Earth with our echoes.”

“How can we know that?”

“We cannot know, that is all that I cling to. We are doomed, Kerris Rat, but there may still be time to save Earth.”

“Garbage, Andrean Wolf. I have a . . . a feel for Enigma. It does not threaten me.”

“I have a feel for Enigma as well, and all that I feel is menace.”

“Wolves are outsiders, they do not have empathy as rats do. Nobody is better qualified to cope with a more advanced species than someone with a few rat attitudes.”

“Then teach me, Kerris Rat. Teach me before it is too late.”

I submitted a proposal to return to where we found the mechanical arm. Andrean signed off on my proposal, but was distracted and remote, like a terminally ill patient who was focused on the approach of death. I took a scout parasail, which was just a seat frame, an impeller, and some controls hanging beneath an airfoil filled with hydrogen. I had a supply cache that would last a week, and the seat could be extended into a sleeping bunk.

Anchoring the parasail presented me with a dilemma. Were I to attach a tether to one of the spires, it would act as a damper when it vibrated in the wind. Use the electric impeller to hold my position, and there would be a low hum to interfere with the sounds from Enigma. Positioning myself above the spires, I turned off the impeller and prepared to measure how fast I would drift with the wind. To my astonishment, I did not drift at all. Many hundreds of millions of years ago, something had anticipated that a visitor might try to hover at that place, and had designed the buildings to produce a wind anchor.

Sitting on the platform, I exposed myself to Enigma’s sounds while monitoring my brain activity and hormone levels. I found definite anomalies, but could not understand them. Enigma’s builders had never seen a human, yet they could control me. I was aware of the control, perhaps because I was a chimera. No template human had descended to Enigma. What would happen if Leonne was exposed to what I was experiencing? I stayed at that position for three days.

It is said that the most effective raids take place in the small hours of the morning. I had developed a habit of waking an hour or two before dawn and looking up at the stars while listening to Enigma and feeling its deeper sounds reverberating through my body. Something f lashed for a moment at the celestial equator, exactly where the Turing was positioned. Immediately I sat up and checked my Earthlink, whose alarm had started beeping. The downward poll signal was dead. This meant that the upward link, with my brain telemetry, was going nowhere.

I keyed the manual link at once. There was no response. I turned the imager to the sky and boosted the resolution all the way. The Turing was still there, but amid a twinkling cloud of fragments. At this distance I could not tell what had been damaged. I kept transmitting, but was returned only hiss. The Cumulus and Nimbus relied on the Turing to communicate with each other, and with me.

“Anyone, can you hear me? This is Kerris Rat, over!”

Silence. Minutes passed. I continued to transmit. Suddenly I got a response.

“Kerris, can you hear me, over!”

It was Leonne, with a very weak signal.

“Leonne Sapiens, I receive you. What happened? Over.”

“An ascent rocket rigged with power packs and scrap metal. It was meant to be a sample delivery. When we saw that it was coming at us full velocity, we managed to turn the starship so that it impacted on the Earthlink module. That dispersed the blast, but killed Earthlink. Over.”

“Who sent the rocket? Over.”

“The Cumulus. Over.”

“The Cumulus fired the rocket? Over.”

“Confirmed, confirmed, and both landers have since self-destructed. We managed to rig comms, but only you are responding. Over.”

It took little effort to work out what had happened. Andrean had spent days struggling with Enigma’s influence. Like me, he had failed. Unlike me, he had despaired. He had not been able to destroy the Turing, but he had broken the link. As far as Earth was concerned, we were dead. Seventeen years in the future, our echo clones would be revived. My last memory of Enigma would be of looking up at the night sky, blissfully unaware of any problem.

“Kerris Rat, are you still there? Over.”

“Leonne Sapiens, this is Kerris. Over.”

“Becter Lattice has got the sensors working again. Thermal wavelengths show that the wreckage of both landers has vanished into the funnels of the city. There is one anomaly left. It looks like a liaison parasail, traveling at about one hundred miles per hour and heading straight for you. Over.”

It had to be Andrean. He would be coming to save me from Enigma, the same way he saved everyone on the Cumulus and Nimbus.

“Leonne Sapiens, I have a bad feeling about this. Over.”

“Have you any mobility? Over.”

“I can flee at the same speed as the incoming parasail. Over.”

“Kerris Rat, you are cleared to flee or fight, according to your judgment. Over.”

Flee or fight. That was what Andrean would expect. There was a third option, however.

“Leonne Sapiens, stand by. Don’t be alarmed when you lose my signal. Over.”

After engaging the impeller and advancing it to full power, I stepped off the parasail.

I fell into the blackness of the funnel. It was about a hundred feet before I hit the steep slope and plunged down into its absolute darkness. After the first minute I turned on my helmet light, but it showed little. The deep, soothing, musical chords and flourishes from the city’s airways were continually with me as I descended.

My personal doppler radar unit gave my speed relative to the oxide-slick surface, and from this I could calculate distances. At three miles I entered a vast cavern that seemed to act like the soundbox of a guitar for all the tunnels that fed into it. On the roof were drawings and script, glowing down as a different texture in the oxide layer. Landers and aliens were depicted, and I even recognized some of the surface features visible from my base. The graffiti of other visitors, I decided as I slid into the next tunnel. Obviously there were no damage control inhibitors down here. Minutes later I entered another graffiti gallery, then another. Were all visitors meant to leave some similar testament, I wondered, or was it optional?

I scanned and recorded what I could as I plunged onward. In a few minutes I had learned more about the alien races of our galaxy than in the rest of human history put together. Gallery after gallery flashed by, all covered with imagery and script from earlier visitors. I passed the five-mile point. So far I had dropped only two miles vertically, but now the inclination of the tunnels began to flatten out, and with this my speed slowed too. There were dozens more galleries decorated and inscribed by earlier visitors, but traces of the alien machine’s descent continued to be visible as well. More than once the thought that I might have made a terrible mistake by jumping passed through my mind, but rats survive by taking chances. Clever chances.

After ninety-one miles of travel and at seven miles depth I finally slid out into what resembled a vast indoor sports stadium. The floor was ankle deep in powdery dust that flowed like black mercury. Shapes were visible, some towering, others mere scraps. One dark shape about the size of an old-style automobile was all ridges, scales, spikes, and mechanical arms.

It had the right dimensions for whatever had fallen into the funnel that I had entered, and it was stylistically identical to the mechanical arm.

For once the archeological evidence was absolutely beyond doubt. Five shots from a plasma weapon had hit the craft, all of them passing through the pilot—who was now just a skeleton in an environment suit. Both of the mechanical arms were attached and undamaged. Scattered about that vast chamber I soon found fragments of another, identical craft, one that had apparently exploded. In the very remote past the aliens had moved beyond rational discussion of Enigma. It was the second craft that had left its arm on the surface.

Words are not adequate to describe how it felt to be working in that place. The only light came from my helmet, but sounds were all around me, echoing down for miles through Enigma’s warren of caverns and galleries. As I had suspected, solid jetsam found its way down here, but the chamber was also built for the dust of eons to settle out.

Even though rats are bold, we are not fools. A cluster of spiky violet crystals about the size of a basketball floated enticingly just above the dust. I was about to reach out to it when I had second thoughts. I tossed a scrap of metal at it instead. The metal vanished. No bang, no flash of light, it just ceased to be. Not far away was a sphere of nothingness. Not a single gleam or highlight was visible, it was just a depression in the liquid dust. I skirted it carefully. My foot discovered a badly corroded device that resembled an assault rifle built for a squirrel.

Later analysis would show that the dust was partly from interstellar micrometeorites falling over hundreds of millions of years and partly oxides from the surface. Enigma’s surface bound with water and carbon dioxide, removing the products of our respiration from the atmosphere, to drift down to these dust traps. Enigma passively maintained itself to perfection.

With the caution of a rat scouting an unfamiliar kitchen I circled the intact vehicle. The vital parts were coated in a smooth material that looked like chrome but felt like plastic. It apparently did not react with oxygen, and so was in pristine condition. I then realized something even more fundamental. The engine was no more than a force-field balance. My backscatter scanner told me that it was like the Turing’s antimatter resonance converter—except that there was no antimatter. From the mechanical arm I had learned how to find and release the access plates in dragoncat devices. I now methodically removed the vehicle’s plates in order to trace the damage from the retaliation shots. Before long I accepted that repairs were way beyond me, and turned my attention to the other artifacts in the chamber. To my surprise I found that most were intact.

Andrean was traveling slowly as he entered the chamber. I had suspected that he might try to follow me once he caught up with my empty parasail, and so had set up a short-range radar sensor to give myself a few minutes of warning. I hid behind some wreckage in case he arrived shooting. My visor’s infrared display showed him as a shape crouched warily amid the swirling dust and alien machines.

“Andrean Wolf, I hoped you would visit,” I said in the darkness.

“Kerris Rat?” he asked, seeing what was visible of me as an infrared glow, just as I saw him.

“The original Kerris, accept no echo. They lead very sheltered lives in those suspension tanks.”

“No heroics please, my beacon mortar is armed,” he said. “One move and I shoot.”

“I am marooned down here until I starve. Why should I care?”

“You are not moving. This tells me that you do care.”

“Then I invite you to put my ghost to rest,” I said, hoping there was no tremor in my voice.

Andrean considered this option, allowed some moments of silence to pass to see if my nerve would crack, then realized that a lengthening silence meant loss of face for him.

“We are both ghosts, so we have all the time in the world,” he said, still wary.

Now I had the advantage. There is nothing that a guru, prophet, messiah, or alpha wolf wants more than followers. Even one will do. Andrean would be regarding me as a challenge.

“Who else is still alive?” I asked.

“The Hounds have sacrificed themselves.”

“How very dog.”

“Eagle and Fox were not as willing, but they too are dead.”

“You failed to destroy the Turing.”

“We broke Earthlink. That was enough. My echo will awake in seventeen years and explain.”

Andrean switched his helmet light on and shone it at my face across the distance separating us. Coming across to me, he satisfied himself that I was not armed. Only now did he glance over the detritus in the chamber.

“So even an eternal city has junkyards. Is that why you came down here? To examine junk?”

“Of course. Junkyards are the lifeblood of archeology.”

“I suppose you will try to tell me you have discovered Enigma’s secret.”

“Work it out for yourself.”

“Perhaps I will. We have plenty of time.”

“Until the food runs out and my portable recycler degrades.”

Killing me would mean he was left alone down here. For someone intending to suicide, that should not have mattered, but perhaps he hoped to lure those in the Turing down to help.

He sat down on a device with rather Gothic-looking outlines that seemed to serve no purpose at all. His helmet light panned across a mixture of wreckage and ancient, intact equipment amid the swirl of black, liquid dust.

“Enigma was set up specifically to be found and visited by civilizations that have just obtained the capability of interstellar travel,” he began.

“Very good, but why?” I asked.

“The visitors learn the lesson, then take it home. Their races then go on to the destiny that Enigma has decreed. That message is on the winds, in the colors of the spires, towers, and buildings, within vibrations and tremors in the surface, and in many other effects that are probably too subtle to notice.”

The rat had the wolf in a dialogue, but for how long?

“That’s all?” I asked.

“Enigma is the ultimate evangelist. Races come and go, but Enigma is eternal. It is a message given form. It travels through space, indestructible, forever ready to spread its message. It has sunk its hooks into my mind, but it has not yet seduced my will away.”

“Or mine.”

“True. We are chimeras. Perhaps Enigma’s builders did not expect chimeras. That was pure luck. That allowed me to save Earth.”

“Then why come down here to kill me?”

“Because I do not know my enemy. Your recycler can keep you alive for a few days longer. In that time Enigma might grant you the power to . . . perhaps to teleport to Earth by a mere act of will. No, best to end it all here.”

“One out of three.”

“What do you mean?”

“Enigma has been attracting visitors like us for hundreds of millions of years—true. Enigma has a message—false. Enigma seeks to influence us—false.”

“Of course Enigma influences us. Why else would we do the repairs to its buildings?”

“So that we can be heard.”

“There is nobody to hear us.”

“Ah, but there will be, millions of years in the future. Reading the lattice databanks in the repair sites and visiting these chambers and the graffiti galleries is better than visiting the home worlds of the earlier visitors. They all arrived within a few centuries of their industrial revolutions. Their inscriptions, time capsules, and discarded equipment are still comprehensible to us.”

This was a very rat perspective. The wolf pondered this.

“You have my attention,” he conceded.

“How often does a civilization achieve interstellar flight in this galaxy? On the basis of what we have found on the surface, perhaps once every five million years. Now ask how long a civilization lasts until it becomes something unrecognizable to people at our level. A thousand years? Do the math and the chances of us meeting another space-faring race are two in ten thousand, but probably less.”

“This tells me nothing about Enigma.”

“Oh, but it does. Visits to Enigma are the only time alien civilizations will ever have anything in common. A million years earlier, and healthcare means scratching fleas, security is trying not to get eaten, and entertainment is scoring a screw when the alpha male is not looking. A million years later, and we are totally unrecognizable. Enigma is a beautiful but puzzling piece of work, designed to draw attention to itself and attract visitors. Here we can meet the hundreds of alien races who have come and gone before us.”

“This does not make sense,” said Andrean. “The chambers and tunnels beneath Enigma are inaccessible, unless you do a one-way slide like we did.”

“I have reviewed the scans I did as I passed through the graffiti galleries and surveyed the tech in this chamber. Humanity appears to be the first space-faring race ever to visit Enigma without using some type of gravitational inversion. All the other visitors could fly down the tunnels using backpack units. We need parasails inflated with hydrogen, and they don’t fit.”

Andrean said no more for quite some time, so I was fairly sure that I had made sense. Humanity yearns for diversity. For a lack of aliens they created the latticeheads, poochers, androids, and of course we chimeras. Long ago, Enigma’s builders must have known of some innate need for intelligences to meet other intelligences. They thought it so important that they left us Enigma, so that even when separated by millions of years of evolution, development, and change, we could still know the other visitors as friends and colleagues.

“So I have destroyed humanity’s chance to use Enigma, Kerris Rat,” Andrean finally admitted. “Is that not true?”

“In seventeen years your echo will awake on Earth and tell everyone how you destroyed the expedition and murdered us originals.”

“I did it to save humanity.”

“But humanity was not in danger.”

“When we get back to the surface I will transmit a retraction.”

“How? You destroyed Earthlink, and we are marooned down here.”

“Then what can we do?”

“We can leave our own message. Do you have anything to say to the next visitors, Andrean Wolf? Scratch it on the wall if you do.”

Again he said nothing for some time. When he did speak, it was a lateral instruction, such as a rat might resort to when trapped.

“Down here, most of the artifacts look undamaged.”

“I think this place is meant to be a sort of archeological trade fair. Most visitors leave something.”

“Some of them are floating above the ground. They must be gravitational inversion packs and sleds. We could use those to escape.”

“It takes weeks to master alien equipment, if it can be done at all. We have days.”

“The batteries I brought down as weapons will last your equipment for many weeks, Kerris Rat.”

“But you have no supplies, and mine are almost all gone.”

“Then I had better provide something for your recycler,” said Andrean as he raised his beacon mortar to his head and shot himself.

As it happened, I took five weeks to master one of the artifacts that had remained functional after uncounted millions of years of dust, darkness, and pure oxygen. Using it, I was able to return to the surface, then seal my environment suit and reach the Turing and other survivors in orbit. In the years since then, we have been able to build a new Earthlink and explore some of Enigma’s caverns. There are enough caverns to last many lifetimes, so it is better than exploring the galaxy itself. All of our findings have been transmitted to Earth, but will anyone listen? I have a feeling that they will heed Andrean’s warning and ignore all new transmissions from Enigma.

I no longer care. We are leaving a chronicle of Earth’s history in a lattice databank embedded in a meteorite pit repair and a mural on the roof of a gallery deep within Enigma, along with a sample of our equipment in the chamber where Andrean killed himself. I am writing within the mural of how we were the boldest of the visitors to Enigma, using the most primitive and dangerous of technologies to cross the chasm of distance from Earth. I know I will have appreciative audiences, even when humanity has progressed beyond the comprehension of beings like us.

After all, that is what Enigma is for.