The diskworld was a very strange place indeed.

Bram, weighing no more than an ounce or two, stood at the front of the landing ladder and looked out across the red twilight at a thin slice of landscape that stretched away into darkness.

Its edges were sharply defined against the starry night. Strictly speaking, there was no horizon at the end of it; the bleak, uniform vista dwindled to a vanishing point long before the eye could reach that hypothetical sykline some millions of miles beyond.

It gave Bram the illusion of standing on a very high, infinitely long ridge. Ahead was a flat, narrow plain of rubble that turned into a needle point piercing the black sky. On either side of him, not many miles away, was a sheer cliff that dropped down ninety million miles to a chasm filled with stars.

His weightlessness contributed to the dreamlike feeling of the place. The next person down the ladder jostled him unintentionally, and they both drifted a foot into the air before settling to the ground again.

Bram glanced into the other's faceplate and saw by the blue glow of the helmet telltales that it was Jao. For once the red-bearded physicist was speechless. Both of them turned by common consent to look at the inner rim of their thin-sliced world.

The universe of stars gave way to a sky erased by stray luminescence, over what appeared to be a geometrically straight edge with no hint of curvature.

The brink of the world.

The great disks rose like goblin faces peering over the precipice, glowing a dull red of dying embers. As this queer world turned, they would rise in unison until they filled the sky. Even now, the big one ahead of them in orbit showed an angular diameter of fifty degrees, a hundred times wider than the sun would have been had it been visible.

From the present angle of view, almost forty million miles above the plane of the sun, one looked down on the inner disks. The three in the next orbit inward faced each other in a circle, like a conference of goblin children. Only one of these showed its glowing face; the other two were circular blots of darkness. Still farther inward hung more disks, getting smaller and smaller.

“I think I figured it out,” Jao said.

“Figured what out?"

“How to manufacture a diskworld."

“How?"

Jao affected jauntiness, but his voice shook a little. “Oh, spin-up, foamed materials, superfilament, anchoring masses. I'll tell you more when the geologist's report is in."

Bram looked across to where a squarish space-suited figure on its hands and knees was chipping away at rock with a little hammer. Each blow tended to lift him into the air, and then there would be a wait until he was sufficiently anchored to strike again; it must have been a maddeningly frustrating way to work. Enry had wasted no time. He had started collecting his samples only a few yards from the ship.

“What do you say, Enry?” Bram said.

His radio crackled. “Looks like ordinary rock so far,” Enry's voice said. “Under a layer of dust."

“Yar, from the spin-up,” Jao countered. “Plus seventy million years’ worth of micrometeorites. You're going to have to dig a lot deeper before you get to what this planet's made of."

“Which is?"

“Mostly nothing. Wrapped around gases—oxygen, mostly, I'd guess. Combined with aluminum and probably carbon. You'll have to get a chemist. But I'll tell you this, Enry-peng-yu, when you get to it, it's going to be a job taking the sample."

Enry grunted and continued his chipping. He was gradually working out a low-gravity technique—striking his little outcropping from one side, then quickly reaching around to strike it from the other, and staying more or less in orbit around it.

“The rest of the answer's there,” Jao went on, pointing at the moon overhead.

Bram raised his eyes to the zenith and instinctively wanted to duck his head. Everybody did. The ellipsoidal moon was so close—only a few diameters away—that it seemed in danger of falling.

You didn't have to look up to be conscious of it. You could almost feel it hanging there with its pointed end aimed at your head. Feel it literally, perhaps. Its gravitational pull would not be insignificant compared with the diskworld's feeble tug at the rim. Perhaps the fluids of the cells sent a message to the brain.

The pockmarked body measured scarcely a hundred fifty miles through the long axis. It might once have been an asteroid towed here by Original Man, Jun Davd had suggested, or a smaller moon of one of the dismantled gas giants.

There were artificial structures on the underside of the moon, visible even to the naked eye—a distinctly geometric jumble at the lower tip, with four enigmatic hairlines converging on it from the satellite's waistline. The airless clarity brought it tantalizingly near.

“It makes you feel that you could almost jump up and touch it,” Bram said.

Jao chewed a hairy lip. “You know ... I bet a space-suited man could reach the moon by jumping,” he said in a serious tone. “Assuming he could jump with an initial velocity of, oh, sixteen feet per second. Escape velocity ought to be somewhere around there. The surface gravity here's about like a small asteroid. Like that comet head we visited.” His eyes almost clicked as he started doing calculations in his head. “Suit jets would help,” he conceded. “The trick would be landing safely on the moon, with only a pair of legs to come down on."

“It might be quite a crash,” Bram said. “How far would he have to fall after capture—about a thousand miles?"

“Less than that."

“We'll visit the moon after we get organized here, I promise you. But I think we'll do it in workpods."

“There might be an alternative."

“Huh?"

“We might be able to get there in climbers. We'll know after we get to the ruins."

The ruins—or their apparent focus—lay directly underneath the lower tip of the ellipsoidal moon. Lydis had wanted to land closer to them, but Jao had insisted that she land at least fifty miles away. “It might be dangerous,” he had said, but he had refused to say why. Bram had taken him seriously enough to order Lydis to comply. The distance would be inconvenient, but they had brought along a pair of walkers adapted to airlessness and low gravity.

“What are you talking about?” Bram asked.

“See anything over there? Use your top magnification."

Obediently, Bram searched the distant ruins with his helmet telescope. The liquid crystal display emerged from its clear plastic sandwich and formed a circular image in front of his right eye. He squinted and adjusted the focus.

“I don't see anything."

“Turn up the contrast."

“I think I see some kind of streak or scratch. It's hard to be sure. I think it's in my helmet ... no, it stays put when I move. It may be a beam of light or a reflection. It's pointing straight up in the direction of the moon."

“That's it,” Jao said.

“That's what?"

“Oh, no. I'm not saying. I'm not sticking my neck out till we get there."

“Watch out!” Bram's suit radio said.

He stepped to one side and saw Lydis and Zef wrestling one of the walkers out of the hatch. They let go, and it floated down to the ground, where it unfolded, shook itself off, and inflated its passenger bubble. The biodevice was a tried and true version of the basic model the Nar had used for airless planetoids and nonrotating space structures. Its fragile, elongated frame would not have stood up under any semblance of real gravity, but it was strong enough for places like this. It had a submetabolism that worked on hydrogen and oxygen, and besides supplying energy, the auxilliary system had water and oxygen to spare for passengers.

“Well, let's not waste time,” Jao said, with a hop and a dive toward the vehicle. “Did anybody pack a lunch?"

Enry was engrossed in his work. Now he was putting dust samples into little vials. Ame came bounding over from a fissure she had been studying. “That's more like it,” she said. “Wait till I get my kit."

Lydis drifted down the ladder and stationed herself in front of the spidery biovehicle. “Hold on,” she said. “We go out two at a time, at least till we know more about this place, and we keep the voice and homing circuits on at all times."

“What d'ya mean?” Jao said. “The walker'll carry three."

“Sorry,” Lydis said. “That's the way it's going to be."

Jao assumed an expression of great regret. “Sorry, Ame. You can take the next trip. Do you want me to bring back any rubble samples for you?"

Ame sputtered. “We're going to have a first look at the ruins, and it needs someone with some archaeological and paleontological training.” She appealed to Lydis. “Isn't that so?"

“I'd say so,” Lydis replied.

“Well,” Jao said. “Your daughter has spoken. I guess it's Ame and me. Sorry, Bram. I'll give you a running report over the radio."

“Not a chance,” Lydis said firmly. “Neither your nor Ame is qualified on a walker. Bram's the driver."

It was Jao's turn to sputter. “There's nothing to steering one of those things."

“There's too much trouble an inexperienced driver can get into low gravity,” Lydis said. “You could turn over. Bounce it too high and come down the wrong way. Misjudge a ravine."

“Sorry, Jao,” Bram said. “You can have the second ride. I'll find out what that thing is. And give you a report over the radio."

The walker loped across the jagged landscape, bouncing upward in great buoyant swoops that ate up the miles. Bram, with an occasional corrective jerk of the reins, kept a watchful eye through the inflated bubble on the route ahead. The tumbled lines of rubble they had to cross were not really dangerous to the walker, which was nimble enough to compensate for its stiff-legged gait when it came down wrong-footed on a boulder or crack. But of course it had no long-distance judgment.

“It's shivery,” Ame said, glancing toward the great glowing hump of a disk that rose out of the ground to their left. As dull and rusty as the light was, it cast long gloomy striations of shadow across the stark plain.

“Shivery?” he teased her. “Is that some sort of technical term you paleontologists use?"

She nestled for comfort against him on the narrow bench. “It's been dead and broken for millions of years. But I feel that it's been waiting for us."

“It has."

“And that it's watching us right now."

“Nothing could live here."

“We do. And this thing we're riding in sort of lives."

“You're letting your imagination run away with you. But that's not surprising. This place is haunted. By the entire human race."

“Yes.” She shuddered. “It's like our own graveyard. We're supposed to be immortal. But so were they."

“That's why it's important to find answers here, Ame. And that's your job."

She shook off the mood with an effort. “A job for more than me and Enry. We're going to have to develop a real science of archaeology very quickly. We've never had the subject matter before. We don't want to blunder about, destroying knowledge."

“How do we go about it?"

“We'll need a large labor force from the tree,” she said briskly. “We'll have to establish a grid first, and a cataloging system. The librarians can help there, and everybody else will have to pitch in. Chemists, cultural scholars, everybody.” She challenged him with a direct gaze. “I can hardly wait to get a real team here and start the dig. How soon do you think that will be, Bram-tsu?"

“Right away, if everything looks all right. We'll spend a few days here first—find a good place to set up a base camp, get an idea of the layout. Lydis ought to be able to move the ship a bit closer. That thing up ahead isn't a danger now that we know where it is."

The walker was at the top of a leap, and as it drifted slowly down, both passengers looked ahead through the bubble. The elusive streak at the center of the compound still could not be seen with the naked eye, even from a few miles away. But a couple of stops during the approach and a look through the helmet telescopes had confirmed that it was still there.

Bram had tried bouncing light off it from a hand laser, while Ame made photometer readings. Slashing back and forth with the beam, he had still obtained readings at what a rough triangulation told him was a height of over twenty miles.

Whatever it was, it was indubitably solid matter, and it reached straight up.

“Stop here,” Ame said. “I want to look at something."

Bram reined the walker in. It reared up in the low gravity, then its front legs settled into the dust. Bram made it kneel, then followed Ame out through the lips of the bubble.

It made a primitive air lock, but it was the best that could be done within the limitations of the scrawny bio-machine. Very little atmosphere was lost if you managed the egress properly. You learned the technique quickly—arms stretched out with your head tucked between them, as if you were diving, then squirm the rest of yourself through sidewise, while the fat inflated edges sealed themselves around you, and a quick pop as you drew your foot through. He and Ame had stayed in their suits with their helmets on even though the bubble was fully pressurized with a breathable atmosphere of fifty percent oxygen. Lydis had insisted on that for safety's sake.

Ame headed for one of the low ridges of rubble that crisscrossed the area, as she had done on previous stops. It looked no different from any of the other ridges of rubble as far as Bram could see.

“What is it?” he asked.

“Another rooftop,” she said. “Pretty intact under there, I should think. A warehouse or distribution center, maybe, from the size of it and from the way it's situated—you can see how long that unbroken ridgeline goes on."

“But why—"

“Come on. This way.” She had already planted a locater beacon in the debris for future reference, and now she scrambled up a low slope, sending up clouds of dust and chips that hung there in the inconsequential gravity.

“Careful of your suit,” Bram cried, but she had already disappeared over the edge. With a sigh he leaped after, soared over the peak with his legs tucked up, and dragged a toe to put himself down just on the other side. Unexpectedly, he found himself standing next to Ame on a forty-five-degree slope that ended at the base of what was ummistakably an uncovered wall of stone one hundred feet away.

“I thought I saw it when we were at the top of that last jump,” she said complacently. “Collapsed roof. Quake, maybe—we'll have to ask Enry how quakes would work on a body with stresses like this one. Or maybe a meteorite strike. Look, it took four levels with it—it must be all tumbled down underneath there."

She pointed, and Bram saw the broken ledges on the wall opposite, each with its cap of dust.

“And that will tell us how deep the regolith lies on a body like this one after we measure the slump,” she said. “You know, there must have been a lot of leftover junk in this system after Original Man got through with his construction project. We've got seventy million years’ worth of impact debris and dustfall. Lot of digging to do. Small bodies tend to lose mass because of high-energy impacts. The gravity doesn't hold on to the stuff that fountains up. But on a body like this, even though the surface gravity is low because of rotation, there's still the attraction of all that mass. The impact debris has no place to go, really, and over the eons it settles down in a slow rain and stays."

“You've been studying your astronomy."

She gave a pleased laugh. “It's the same as geology in a place like this, isn't it?"

“What do you expect to find under all that rubble?” He gestured at the tipped slope they stood on.

Her eyes shone. “Fossils, if we're lucky. There'd be organic material if this was a food depot—or even if people lived or worked here, away from the operational center. People leave garbage. And garbage means mold, bacteria, microfossils. Maybe even the bones of vermin. Original Man must have had vermin."

Bram remembered a childhood tale: The Dappled Piper of Shu-shih.

“Yes, indeed,” he said. “They called them rats."

“Member of the order Rodentia" she said with a frown. “They're in the mammal list, but Original Man doesn't have much to say about them."

“I'll settle for a few dessicated bacteria. Would there be any DNA left after seventy million years?"

“Maybe. This place isn't cold. But it's airless and dry. Original Man ressurected something called Tyrannosaurus rex from a bone fragment after a similar period. In his twenty-first century. They kept them in zoos."

He caught something of her excitement. “What a find a few bone fragments of Original Man would be! If we could do some DNA sequencing on a big enough sample, we could find out if he edited us before broadcasting our genetic code."

“We don't know his burial customs. But millions of people must have lived here over a period of time to operate the beacon. There would have been accidents ... illnesses that got out of hand ... the rare individual who was immune to the immortality virus—” She broke off, abruptly aware that Jao would be listening through the radio link.

“We'd better get going,” Bram said. “You've left a marker; we can send an excavation team later."

But Ame was unclipping a folding shovel from her belt. She flexed the stub of a handle once to activate the memory plastic and an instant later had a proper shovel. “Let's see how deep the regolith is where it's slid down here,” she said. “Help me clear some of this away."

Bram worked with his gloved hands while Ame shoveled, and within a tenth of an hour they had uncovered a smooth, hard gray surface.

“No miracle materials, those,” Ame said. “They made the walls and roof of ordinary melted and poured stone. They could afford to mold it thick enough to cover expanses like this. There was plenty of stone, and power to spare before they switched on the transmitter."

“Twenty-three sextillion kilowatts, Jao figured,” Bram said. “Trillions of times as much energy as the entire Nar civilization had at its disposal. It's a little disappointing to find that their building construction was so prosaic."

“Sophisticated megaliths,” Ame said. “That's what they are. Great slabs meant to outlast eternity. Only this one didn't."

She rapped the end of her shovel sharply; hydrogen atoms spilled from the reservoir they had fled to, preempted bonds again, and once more the shovel handle shrank to fit into her belt. She occupied herself for a moment chipping a rock sample from the slab. “I'll take this back to Enry for analysis,” she said.

She bobbed to her feet a little too quickly, and Bram pulled her out of the air. “Ready?” he asked. He was anxious to return to the walker and continue toward the apparent center of the complex.

“Just a minute,” Ame said.

She looked down the rubble-strewn slope of where its edge abutted the vertical wall and studied the V-shaped trench it made. “There's broken rock in places along the edge,” she said. “If any of them correspond to broken sections of the underside of the slab, we could get underground without digging."

“No,” he said. “We're not going to crawl through caves without any backup. It's too dangerous. This place will still be here when we get back. Let's get going. We're wasting our air supply on the outskirts."

“As long as we're here, let's just take a look," she said.

“All right."

He gave in and followed her down the slope. He didn't like it. They were in a deep groove, cut off from sight of the walker and the never-ending landscape. Only the stars burned overhead.

Ame was unconcerned. She played the light of her torch along the join of the two surfaces. Color vision returned, showing Bram vitreous streaks of green, brown, and yellow mixed with the gray. Even to the naked eye it was apparent that the rubble had slid down the slope to cover any possible cracks to a depth of many feet. It would take a lot of work to clear it away.

But he was wrong. Ame's torch played on a gaping black aperture that ran down the rocky crease in a spot that seemed remarkably free of rubble. In fact, the rubble seemed to be piled higher on either side of it.

“It goes all the way down,” she said. “About twenty feet to where the floor is. Big enough to squeeze through, and then there's a sort of triangular tunnel made by the edge of the roof slab and the angle of the floor and wall. The tunnel's clean—hardly any debris to clear away. I wouldn't have expected that. The roof must have collapsed with miraculous precision. Half our work's been done for us already. And when we explore the whole length of the cleft, we're bound to find places where we can get through into the main part of the ruin.” Her voice rose with excitement. “Acres and acres of undisturbed ...anything! Bram-tsu, why don't we just—"

“No,” he said firmly. “We're not going to go crawling in there now. For one thing, we'd be out of radio contact. Come on, Ame. We've seen everything there is to see for the moment.

“I suppose you're right,” she sighed. She played the beam of her torch in widening spirals around the entrance. “But I don't understand where all the rubble went."

Then they saw the footprints.

The tracks converged on the hole from all directions. Heavy traffic. The reason they weren't obvious in the immediate vicinity of the hole was that they became too thick there, obliterating outlines and churning up the dust. Besides, getting in and out of the hole meant belly crawling, further erasing any tracks.

But they were very plain farther away.

They were longer and narrower than an ordinary human footprint, but they covered about the same area and presumably would have supported a body of similar weight. The foot that had made the imprint had been encased in a tubelike boot with a ridged underside.

When he was able to catch his breath he said, “How long ago?"

Even his untrained eye could see that the outlines of the footprints were not as sharp as the prints he and Ame had left.

Ame produced a tiny measuring stick and compared the depth of the two sets of prints. Then she poked the rod into the dust in several places.

“They're recent,” she said.

That startled him. “How recent?"

Her features worked within the helmet. “We'll have to assume that the dustfall on this world has been diminishing during the last seventy million years, as the disks swept out their orbit. Dimishing on a logarithmic scale, maybe. Most of the dustfall must have taken place in the first few million years. But the roof must have collapsed, too, within a few million years of the time when Original Man abandoned the place, because of the later buildup that replaced the dust that slid down into the crevice."

“Ame—how recent?"

“It could have been within the last thirty million years."

Bram swayed in the low gravity. “More than forty million years after we thought the human race died out,” he whispered. He grasped her space-suited arm. “Could these prints have been made by a human foot?"

She shrugged. “Depends on what you want to consider human. It took the human foot only a few million years to evolve from a grasping organ that looked something like our hands. I suppose that in another forty million years, it could have evolved into something that looked like that."

She splashed her light around the prints. “It's hard to tell what might have been inside that boot,” she said finally. “But the elongated proportions aside, that could be a foot with the normal configuration of heel, instep, and toes. They always bend in the same place, so they had bones. Not like a Nar footprint that varied from step to step."

“They brought animals with them."

The light revealed meandering chains of shallow little paw prints, hardly larger than a human thumb. Then it struck Bram.

“What kind of animal could live in vacuum?"

The paw prints divided into five slender toes. Whatever had made them had been bare to space.

Ame leaned for a closer look. “A terrestrial animal. We've got quite a few drawings to go on. All terrestrial vertebrates had limbs based on a plan of five digits—even those that evolved into hoofs or wings. Bram-tsu, I've seen pictures of paws that must have looked something like these, on little climbing creatures like tree shrews, and raccoons, and ... and squirrels!"

“And rats?” he suggested. “Yes, those, too."

“Could this world once have had air?"

“N-no. Not with the low gravity. Besides, these prints show no signs of weathering. They're perfectly preserved."

Bram stood up. His knees felt weak. “We've never seen another terrestrial animal,” he said. “On all the Nar worlds, we were the only specimen. Now it appears that we're standing on a world that once held at least two more specimens. Let's get going, Ame. The sooner we finish our survey, the sooner you can start digging for fossils."

“Bram-tsu, have you noticed something?” She moved her beam of yellow light around the area, holding it low to cast shadows.

The little paw marks were always superimposed over the footprints. Never the other way around.

“The animals were later,” he said.

“A lot later,” she said. She rested the light on a nearby cluster of paw prints. “Look at these. They're very shallow because of the low gravity and because a creature that size wouldn't have massed very much. They can't be more than a millimeter deep. But even so, every detail is sharp. They're not at all blurred by dustfall. They couldn't possibly be more than a million years old.” She traced the paw prints with the light to where they disappeared into the crevice. “They might have been made yesterday."

It was a ladder to the moon.

Bram and Ame left the walker at the edge of the massive circular housing and walked over to where the two thick ropes rose straight up into the sky, taut as bowstrings.

The ropes were semitranslucent and so thick around that it would have taken six or seven people joining hands in a circle to have embraced them. The bulge of the winding strands was sufficient to have served as a spiral staircase.

“The moon's tethered,” Bram said. “Like a captive balloon."

They stared up to where the cables disappeared into the sky. They were visible, Bram guessed, to a height of a couple of miles.

One of the cars that once had plied the tremendous mooring line was stalled about a hundred yards up, like a bead on a string. It was a flattish ovoid with portholes around the rim, and the beam of torch reached high enough to show it to be painted a jolly shade of red. The cable passed through the car's center. Bram could only guess at the nature of the mechanism that climbed the braided cord—worm gears or ratchets or cogwheels. But there must have been an inner carousel that housed it, to keep the passengers from getting dizzy.

What a ride it must have been! Being whirled upward at thousands of miles an hour. How would they have managed turnover so that they could land on the moon right side up? Was there a way station at the point where the moon's gravitational influence took over? A transfer point linking the two cables? There would have to be one car coming down for every car going up, to maintain equilibrium: One didn't fool around with stresses like these!

His eyes moved across a mile of circular plaza to where a second set of sky ropes had been guyed. One of them had snapped. The end of the cable lay in ruins amid the buildings it had smashed. The dangling end of the rope was visible about a half mile up. The remains of an ovoid car that had slipped off the end of the rope lay strewn across the plaza.

Bram hoped no one had been in it. The disaster most likely had happened millions of years after the departure of man—maybe even millions of years after the time of the narrow-footed visitors. But the remaining set of cables had been strong enough to hold the moon down. The astonishing system had been engineered for redundancy.

Unable to resist, Bram reached out a cautious hand and touched the glasslike rope where it rose out of an encircling collar. He might have been touching a column carved out of solid steel. It was utterly hard, utterly immovable.

“Now we know what those hairline markings on the moon are,” he said. “The moon's wearing a harness."

“Bram-tsu, Jao is going crazy,” Ame reminded him delicately.

“Sorry, Jao,” Bram said, switching on the receiver of his suit radio. “I guess you've been listening to me and Ame oohing and ahing. I forget that you can't see it."

A howl of the purest agony reached him. After a moment, Bram realized that words were embedded in the incoherent gargling sounds.

“Describe it. What are the dimensions? What does the surface look like? What colors do you get when you flash light on it? How's it anchored? Careful of loose threads, if there are any. You could lose a finger."

Bram gave him a brief description of the rope and the surrounding installation. “I can't imagine what it would be made of,” he said. “And I can't see how it's anchored. It just disappears into the ground."

“Yar,” Jao said, breathing hard. “Each thread is a single continuous molecule that reaches from here to the moon. My guess is that it'll turn out to be mostly oxygen bonded to silica, magnesium, and aluminum, with a carbon backbone to help out with all the connections. It'd be harder than diamond and with a higher tensile strength than amorphous boron to start with, and then there'd be some kind of submolecular weaving between adjacent chains ... And, oh yah, you won't find where it's anchored, because it reaches all the way down to the original core of this world, forty-five million miles under your feet. That's because it's only a guide thread—part of the warp and woof that held this world together while they were spinning it."

“Slow down,” Bram said. “I can believe in your tied, down moon because I can see the evidence here with my own eyes—and by the way, you'd better radio Jun Davd right away and tell him that we've solved the mystery of why the moons are lower than they ought to be for synchronous orbit. I'll even accept your endless molecule till a better explanation comes along. But how could it support another forty-five million miles of its own weight?"

“It's the other way around,” Jao said smugly. “The idea isn't to hold the moon down. The moon is what holds the world up."

Bram looked around at an apparently solid landscape. They were near one edge of the rim here. The avenues of rubble stretched to the opposite side, fifty miles away. The rectilinear mounds were higher at the lunar longitude than they had been on the outskirts of the enormous complex—the buildings had been taller and more important here. It had not occurred to Bram to wonder why the moonropes were peripheral and not centered, because, after all, the entire surface of the diskworld was the “equator."

“You're getting too farfetched,” he said, and waited for the next dizzying supposition from Jao.

“Am I?” Jao retorted. “I'll bet you anything you care to name that when we cross that plain to the other side, we'll find another cable car station and another set of ropes. Making an equilateral triangle with a fifty-mile base and its apex on the moon. Wait a minute! Make that a very narrow tetragon! Why not? The angle of divergence is minuscule on that scale. You might as well have parallel tethers. No, wait again! How about spreading the moon terminal still farther apart? At an angle that converges at the disk's core? With a little truing of curves, you could have a ninety-million-mile section of parabola for your. antenna. Bram, we've got to map the whole topography of this disk! I'll bet it has a concave cross section. Hard to detect, but it would make this razor's edge of a rim the widest part, except for the leftover bulge at the hub!"

“I'd have thought that even a few inches of overhang at a height of forty-five million miles would add up to insupportable stresses."

“Don't you see?" Jao's voice exploded in Bram's ear. “This world was built like a suspension roof! It had to be! Otherwise, with the spin needed to keep it from collapsing under its own weight, the synchronous orbital points would have been embedded somewhere below the surface! There wouldn't be a stable surface! All the people and the buildings and the topsoil would be thrown off into space!"

“What's a suspension roof?"

“It was an idea one of the Resurgist architects had for building our sports arena in the human compound. Arthe, his name was. You strung cables from supporting piers and laid roofing material over them. You kept the internal air pressure of the building higher, to bear some of the weight. It was a way to provide a larger interior space unobstructed by load-bearing pillars. Nothing ever came of it. The council was too conservative and decided to stick with a Nar-style shell."

“A whole world built that way?"

“Why not? It makes sense. And it fits the facts. We know this world is lighter than air. About twice the weight of helium on average. And when that average includes a rocky surface and two apparently rigid faces, then we're dealing with an artifact that for all its size is mostly a gossamer nothingness enclosing more mostly nothingness."

“Yes, I remember that Smeth proposed a honeycomb structure or a membrane enclosing a gas."

Jao snorted impatiently. “But how do you build up a honeycomb out of a gas giant's mass without it collapsing into a sphere after the first hundred thousand miles? Even if your honeycomb were as light as hydrogen? Especially when you're starting out that much closer to the center of gravity—not like out here on the rim, forty-five million miles away from it, where we're down to about six decimal places worth of zeros with a one hung on the end of them, and we're staying attached to the surface mainly by courtesy of the local gravity of the crust. As for a membrane, one meteor puncture and you'd have the deflated skin of a world."

“It would take more than one,” Bram demurred.

“This world's had more than one,” Ame said tartly.

“All right, gang up on me,” Bram said. “Go on, Jao. Lydis, are you recording this for Jun Davd?"

“Yes,” Lydis said. “I can always add it to the reserve air supply. After cooling it down."

“Who told you it'd be risky to make a cislunar landing approach?” Jao reminded her. "That didn't turn out to be hot air, did it?"

“Let him finish,” Enry's voice broke in. “It fits in with my seismograph readings. The waves damp out a few miles down."

“Thank you, Enry. I'm glad there's one member of our expedition with a little vision.” Jao continued smugly. “You start with an unremarkable rocky-type body—maybe the core of the gas giant they poured into their parts bin. Next you tow your twelve moons into place, positioning them so that they occupy the same synchronous orbit in a stable dodecagonal configuration. If you don't have twelve leftover moons handy, you fill in with a few hefty asteroids."

“Skip the details for now,” Bram suggested, “or we'll never get there."

Jao made a pained sound. “Then you drop a line from each of your synchronous moons and anchor them at the planet's equator. While you're lowering the lines, of course, you have to keep judiciously raising the moons’ orbits, to keep the center of gravity in the right place. Even with the lightweight filament you're using, the mass adds up as the line grows."

“So far you're describing the construction of an ordinary orbital elevator,” Bram said.

“You recognized that?” Jao sounded pleased. “Not many people knew about that project."

“I worked on a part of the problem at the biocenter,” Bram said. “Ordinary viral monofilament—the kind the Nar used for the bubble car cable network—tested well within the breaking strength limits, but there were still some problems with prolonged ultraviolet exposure that needed to be worked out."

“What's an orbital elevator?” Ame asked.

“You're looking at one,” Bram said, pointing at the plaited crystal tower that rose into the sky with its impaled passenger vehicle still hanging from it like a spitted egg. “The Nar had a scheme for building a number of space docking stations on the same principle. Eventually they looked forward to a whole ring of them around the equator of the Father World, linked together for stability. It was well within the limits of theoretical possibility. But the Nar thought in terms of thousands of years, and there was no particular sense of urgency, oxygen and biologically produced alcohol for shuttle fuel being as cheap as they were."

“The big difference here,” Jao rushed in, “is that Original Man's skyhook used two tethers, anchored fifty miles apart. That was important. Even if they came together at the apex of an isoceles triangle twenty-odd thousand miles up, the slight lean from the true vertical wouldn't have mattered that much. Not with the materials they had available."

“Okay, you've got your twelve moons, bobbing up there like captive balloons, and connected to make a dodecagon—"

“To make a circle, Bram. The line bellies outward."

“Okay, a circle. What next?"

“Next they started spinning the world. Faster and faster. At the same time, they began playing out more of their superfilament. They must have fed it out in a liquid form that instantly hardened—"

“There was a terrestrial animal called a spider that did that biologically,” Ame put in.

“Yah, I wouldn't know about that. Anyway, they probably fed in the raw materials at the poles, from a couple of big gas clouds they had parked out in space. The oxygen and carbon could'ye come from carbon dioxide they siphoned off a hothouse-type planet—there's one of those in almost every G-star system, same as gas giants. That must've been a sight to see—the two big vortices whirling from the poles millions of miles into space, while the tethered moons spun out farther and farther weaving a gossamer web between them."

“You don't think small, I'll give you that.” Bram laughed.

“Now you start extruding your foam—mountains of it, oceans of it, following the network of filaments into orbit, the trapped bubbles of gases blowing the material up to two or three thousand times its volume before the molecules cross-link and become rigid. It maintains the disk shape, reaching a predetermined orbit at the limit of the spin force, with an excess material falling back to the surface. Foam that squeezes laterally through the web shears off, making a nice smooth face. Depending on the altitude, the excess stuff either slides outward or falls back to the hub. It's exactly like the preliminary stages of the formation of a protostar ... or ... or a galaxy! The material settles more and more into a flat rotating disk! But now, with the growth of the disk, angular momentum is transferred and the spin slows down! So you get the stable situation we see here, with the moons traveling just a little faster—or lower—than they ought to be for synchronous orbit and maintaining the tension that helps hold the whole structure together."

He stopped, out of breath.

“What's happened to your rocky world at the center?” Bram asked.

“Oh, that? It's smeared all over the faces of the disk. Some of it's been flung out beyond the rim and fallen back, and we're standing on it. And the rest of it's a plug in the hole at the center of the disk, where the gravity is perpendicular to the disk surface. “It's heavy there, that close to the center of gravity, I promise you!"

“What about it, Enry?” Bram said.

“It could be.” The geologist's voice was muffled; he must have turned his head away from the helmet mike to check data. “I've got samples that could have come from the rocky core of a gas giant that broke up. Silicates that show signs of once having been under tremendous pressure. Millions of atmospheres worth—the kind of pressure that turns molecular hydrogen into metallic hydrogen. The paleomagnetism's interesting. The orientation's every which way. As if the samples originated elsewhere and were scattered all over the place."

“What did I tell you?” Jao sounded smug.

“There's something else,” Enry drawled.

“What?"

“The rocks show that there's a steady leakage of gases from the interior of this ... world. Oxygen, and carbon dioxide, and lighter gases like nitrogen and helium. The rim can't hold on to an atmosphere, of course. But there could be a considerable amount of gas still trapped in the ... cavities that Jao postulates.” There was a moment of silence with an unmistakable frown in it. “More than there ought to be, from the rate of leakage, after seventy million years."

“The gases are subliming off the foamed surfaces,” Jao said quickly. “And maybe off the superfilament as well. Nitrogen, did you say? I'm going to have to rethink the chemistry of it. Plenty of oxygen, that's for sure. Hey, we might be able to tap into it during our stay—take some of the load off Yggdrasil!"

“How far down would we have to drill to tap atmosphere?” Bram asked.

“I don't know. It would take some pretty fancy mathematics to figure out the thickness of the crust, based on too many variables—the size of the original core, rate of spin-up, disk gravity gradients, surface friction affecting the dispersion of material ... I think we'll have to rely on Enry's empirical methods. Theory falls in a case like this. It can't be much, though."

“Those bare paw prints,” Ame said. “Do you suppose..."

“Forget it, Ame. Any atmosphere belched out from the interior would instantly disperse. You'll have to find another explanation."

“There was life here within the last few million years—I'm certain of that,” she said stubbornly. “It's..."

“What's the matter, Ame?” Bram said.

She flashed her light around the base of the moonrope. “Look,” she said.

The tracks had been easy to miss in the permanent red twilight, especially when there was the awesome sight of that crystalline pillar drawing your eyes up instead of down. And the reflected light from directly above had tended to wash out the long, diffuse shadows cast by the horizon-filling sliver of the companion diskworld that rose above the brink.

But once you had noticed them, it was hard to see how the eye had skipped over them. Shallow as they were, they were perfectly plain, like inked thumbprints, a little smudged where the tiny paws had scrabbled in the dust. The myriad trails meandered a bit. But in the end pointed toward the soaring cable.

“They climbed it,” Ame said. “That's where they went. They climbed to the moon."

They had six hours to explore the central complex, Lydis told them. After that, they would begin to tax the walker's ability to replenish their air supply. “I don't want you to use your reserve bottles at all,” Lydis said. “That's cutting it too close. I want you to come in with your reserve bottles intact. Understood?"

“Understood,” Bram told his daughter. He sighed. It had been five hundred years since she had been a little girl, but every once in a while it felt strange to be taking orders from her.

Ame was scrambling happily all over the mounds of rubble, leaving little electronic markers that would give off coded transponder signals when asked.

“Site number twenty,” she dictated to one of them. “Probable auditorium or lecture hall.” She followed with a series of dimensionless coordinates that would be fitted later into a triangulation grid by a computer.

“How can you tell it's an auditorium?” Bram asked. “It's just another dust pile, as far as I can see."

“It's fan-shaped,” she said, tossing him a grin over her shoulder. “We tend to think that public halls are supposed to be circular, with a stage in the center, because of the Nar influence. But this is a much more natural shape for human beings. And see, the focal point—abutting what might be classrooms or administrative offices—is at about the limit of distance from which a live lecturer or performer could be seen to any effect."

Bram followed her around as best he could, climbing in and out of the walker, helping with the measurements, and operating the little portable thumper that located cavities beneath the surface.

“Libraries,” Ame exulted. “I'm sure of it. And museum warehouses and storehouses and depots and vaults for frozen samples. And all the support and recreational facilities you'd need for the population of millions that it would have taken to run this outpost—hydroponic farms, maybe even zoos! This will be a treasure trove for the archaeologists, Bram-tsu! And there'll be middens—we'll find seeds and organic refuse and bones..."

He didn't like leaving her alone while he went off on his own side forays, and at one point he coaxed her into the walker for an excursion to the rim's edge.

“Don't go out any farther,” he warned. “I don't know how secure this thing is."

They were standing on the great skeleton arm of a gantry that extended out over the abyss—part of some sort of transport system that traveled an unknown distance down the face. Bram could see the stanchions that once might have supported an elevator or funicular dwindling with distance till they disappeared.

Hundreds—possibly thousands—of miles down the sheer face began a glittering fairy forest of tiny filaments that swept in a great arc until they could no longer be distinguished against the knife edge that cut the black night ninety million miles below.

“The feed array for the antenna system,” Bram said. “There must be others, equally spaced around the disk, aimed at a reflector at the hub."

By this time they had worked themselves through to the opposite edge of the disk, facing the intergalactic night. The antenna complex was lit from above by ruddy moonlight.

The buried city, limned by mounded avenues of detritus, stretched all the way across the diskworld from rim to rim. And Jao had been right: There was another set of cables climbing to the moon on this side, too.

“So this,” Ame said, “was the voice of the human race?"

“Yes.” Bram dug through the centuries for an old memory. “My teacher, Voth, once said that humankind had learned to tame a sun's power to shout across the gulf between the galaxies, but he couldn't imagine how."

He mused at the phased array, wondering at the scale that would allow its nearer ranks to be seen at such a distance. The elements must be miles high to be even remotely distinguishable—cantilevered or guyed against the topsy-turvy gravity. But that would have presented no problem to a race with moonrope at its disposal. And the gravity would be mild for the next few million miles, anyway. It would be a different story at the hub, where gravity would be crushing. Perhaps there were phase shifters installed at a safe radius. He would send an expedition down the face to see—in a space vehicle. And the physics would have to be carefully worked out so that the explorers would not find themselves slammed against a wall that had become a floor.

Bram shuddered at the thought of the mighty energies that once had been dispensed by that distant forest. In operation, it would have been a microwave inferno that would have sizzled a man to a crisp in milliseconds. No wonder a healthy stretch of no-man's-land had been left—and not just to get past the gravitational edge effects.

Bram inched farther out on the gantry for a better look. Jao was going to insist on a full description. Too energetic a toe push sent him doing a handstand, and he walked a few steps on his hands before his boots settled down, holding on for dear life and being careful not to let go with one hand before he had a firm grip with the other. The asterioid-strength gravity was deceptive, he knew. He still had all his mass, and it was a long way to fall. Already, though he was no more than fifty yards over the edge, he knew that the horizontal component of the diskworld's complex gravity was tugging every atom of his body toward itself in a complicated vector. He would have had to crawl out another million miles or so to feel anything, of course, but it was there nevertheless. But if he were to fall past reach of a handhold, he would be accelerated inexorably—at the dreamlike rate of about one thirty-millionth of a foot per second to start—until, at an unknown fraction of the distance to the center, the reaching forces of the disk would slam him into the tilted wall-scape at a velocity sufficient to abrade him into a long, wet smear.

It didn't help a whit to realize that he'd have been long dead of suffocation, thirst, or boredom before that happened.

Bram stopped his balloonlike four-limbed outward prowl and wrapped himself securely around a thick strut with an arm and a leg while he surveyed the cliff face from his improved vantage point.

There was movement beside him, and then Ame was pressed up next to him, peering past his shoulder into the abyss.

“I thought I told you to stay put,” Bram said.

“Don't be silly, Bram-tsu. I'm perfectly able to take care of myself. What could possibly happen?” She leaned out alarmingly. “Do you think we have enough time to climb down there for a look at some of those caves?"

“No!” he said, hearing himself sputter. In a more reasonable tone of voice, he said, “We'll come back later with ropes and proper climbing equipment and a team of trained outside workers. Maybe we'll round up a few tame climbers from Yggdrasil's vascular system and ride them. And the climbers will wear safety lines, too!"

“It was just an idea,” she said mildly.

She unclipped her torch from her belt and played it over the vertical surface below. Seen up close, Jao's “smooth face” was pocked with great pits and hollows. Looking at this cross section of a world, Bram could see where the crust began, a few miles below, like frosting on a slice of cake. The artificial material beneath was thinly covered with dust, and all sorts of domes, bulges, and the craters of burst bubbles poked above the rubbish of the sundered planet that had been used as a starter.

Closer at hand, vacuum welding over the eons had cemented a rocky cliffside in place. But here, too, even the languorous stresses that the diskworld was heir to had from time to time torn great chunks of material loose and left a pattern of cracks and cavities.

Ame's beam found one of the holes. “I wonder bow deep—” she began, and stopped.

A pair of animal eyes shone in the beam of light for a startled second, then whisked out of sight.

“Oh!” Ame squeaked. She dropped the torch. It seemed to hang in space beside her; the light beam revolving in lazy circles. Ame recovered before the torch had drifted down more than an inch or two, caught it by the wrong end, and got it pointed at the cave again.

“Did you see it, too?” she whispered.

“Yes,” Bram said.

There was life in this place. And it was shy.

They stayed clinging to their dizzy perch until Lydis's radioed warnings about their reserve air supply became too impatient to ignore. But the beady, luminous eyes never reappeared.

“It's hunkered at the back of the cave, waiting for us to go away,” Ame said.

“Or there's a way out through the rear,” Bram suggested. “There may be a whole system of burrows."

She had tried the light in every opening it would reach. Far below, at the limit of the beam, they thought they saw a pair of pinpoints of reflected light for the briefest flash, but it was impossible to be sure. Finally, when Lydis began making threats, they gave up and hauled themselves back along the gigantic crane arm to the security of the rim.

They had left the walker parked a short distance away in a square at the intersection of two avenues of raised gravel. As they approached it, there was an explosion of movement around it, and dozens of small furry forms streaked away into hiding.

Bram gave a start. The little beasts were gone in an instant, before he had time to react.

“We scared them off,” he said.

“They must have been watching us the whole time, everywhere we went,” Ame said. “The ones here got up the courage to investigate the walker when we were gone so long."

A wary little face peered out from around a block of stone, then jerked back as Ame's light beam found it. Bram had a quick impression of huge round eyes, button nose, tiny mouth, and the flash of a bushy tail.

He found himself laughing. “They're curious,” he said.

“They're descended from terrestrial life,” Ame said. “That's for certain. Like every picture I've ever seen. Everything in pairs—eyes, ears, limbs—just like us! And they're furred—they're not only vertebrates but mammals, too!"

“But how do they breathe vacuum?"

“I wonder ... they've had millions of years to adapt to this place. Have you ever heard of whales?"

“I know the word. Stands for something big."

“It was a real animal once. It adapted to a new environment, too. It learned to go for long stretches without breathing."

They were at the walker now. The biovehicle was in the same kneeling position they had left it in. Bram gave Ame a boost, and she hoisted herself up to the passenger bubble. Then she froze.

“Bram-tsu! Look!"

He levitated to a position beside her, and she grabbed his arm. One of the little animals was trapped inside the bubble, scurrying about frantically, looking for a way out.

He stopped her as she as about to insert herself into the bubble. “Wait. Let's see if we can shoo that thing out of there first."

“Why? What harm could it do?"

“I don't like the look of those little teeth."

“It's more afraid of us than we are of it. Oh, look at it, Bram-tsu! It's so small! It's just a little baby! It must have gotten separated from its mother. It's terrified."

Without waiting for a response, she swan-dived through the lips of the bubble. Bram followed, letting out at least a pound of air pressure in his haste.

“The poor thing,” Ame said, reaching for the small creature. It cowered against the far side of the transparent bubble, chittering at them. It was a little roly-poly thing, a ball of soft brown fluff with enormous golden eyes that were mostly round pupil.

“Ame, don't touch it."

“Nonsense! It couldn't bite me through my vacuum suit even if it tried."

She picked the creature up. It squirmed in her grasp, then seemed to give up. A moment later it was in the crook of her arm, clinging to her with four tiny grasping paws.

“It wants its mother,” Ame said. “Look, Bram-tsu, there's a third eyelid for when it's outside."

He bent closer and saw the transparent nictitating membrane flick across the golden eye when the creature blinked at him.

“And little flaps for the ears, too,” he added, noticing the folds of pink flesh that creased reflexively to close off the entrance to the ear canal when he leaned too close, as if the little animal were trying to shut him out of its world.

“I think you're scaring it,” Ame told him.

“No, it's getting used to me."

There were similar little flaps for the nostrils, but the creature's nose twitched as it sniffed at him, and the flaps stayed open.

“I've seen pictures of fur, but I never dreamed it could be so soft," Ame said dreamily. “Sort of like the twins’ hair, only all over. It makes you want to stroke it."

“Ame, you keep those gloves on."

“All right,” she said, patting the little beast with a gauntleted hand. It responded to the touch by snuggling up closer against her and wrapping its tail around her arm.

“We've got to start back,” Bram said. “We'll come back and study them."

“Jorv will be pleased,” Ame said. “All of a sudden, zoology isn't a theoretical science anymore."

“We'd better leave it here. We don't have the facilities for keeping it alive during the trip back to the tree. It might not survive."

“Bram-tsu, I love you. You're a biologist, but it never even occurred to you to take it back as a specimen."

“Well, I...” He flushed, “There'll be plenty of time to study these animals at our leisure, find out what they eat, take tissue samples without hurting them."

It was the Nar influence, he supposed—growing up among beings whose respect for any sort of conscious life was innate. Bram hoped the human race wouldn't lose that trait with the passage of generations, but he had heard a few rather cold-blooded remarks from some of the younger tree dwellers.

“I hate to give it up,” Ame said. “It's so cuddly and cute. You know, Bram-tsu, it's all fluff. Underneath, it's all scrawny."

Reluctantly, she pried the small clinging creature from her body and eased it through the lips of the bubble. Bram saw the little fleshy flaps wink into place over ears and nostrils, and the creature's fur seemed to puff up still further. Then it was floating to the ground with chubby grace, its tiny prehensile paws outstretched for contact.

It scampered off immediately. A larger beast darted from a cranny to intercept it, bowled it over, and nudged it with a button nose to a perch on her back.

“It's found its mother, anyway,” Ame said with relief.

The mother beastie stood up on her haunches to bare her teeth at Ame and Bram, then scurried away with the baby fluffball clinging to her fur.

“I discovered them, and I'm going to name them,” Ame said. “I'm going to call them Cuddlies."