“There's a star in there somewhere,” Jun Davd said through his suit radio. “Its light may be blocked, but it's shining its heart out in the ten-micron infrared range."

Bram clung to a cleat with one gloved hand to keep the trunk's slow rotation from shedding him into space and turned up the magnification of his helmet visor. “A body-temperature star,” he said. “That fits the picture, all right."

He peered past the leafy horizon at a void that was frosty with stars again. After more than two decades of braking, the starbow had separated and strewn its baubles across the sky. The drive was off, and Yggdrasil was towing the probe now, not the other way around.

But despite the magnificence of the sprinkled stars, it was the sight in the center of his image compensator that occupied Bram's full attention.

There was a scratch across the sky—a perfectly straight line, as if a cosmic thumbnail had scraped away the black. Next to the long scratch was a collection of bright squiggles, like cursive writing in an unknown language.

“The straight line's about ninety million miles long,” Jun Davd said. Within the crystal bowl of the new space suit, his dark profile was intent on the distant object. “That's about the same length as the radius of the infrared emission shell the instruments can detect. Does that suggest anything to you?"

“The only astronomical phenomenon I can think of that's that straight and that long is a Type I comet tail,” Bram said. “Except that there's no coma at one end. In fact, the brightest part, if I read the instruments right, is in the middle."

“Yes,” Jun Davd agreed. “And it doesn't extend outward from where the mass indicators say our shrouded star ought to be. It's tangent to it."

“So that suggests very strongly that it has something to do with the structure that's enclosing the star. And that those curved scratches—the arcs and hooks—are part of the same manifestation."

Jun Davd turned to face him: Somehow Jun Davd managed to be limber, even in the bulky envelope of the human-shaped space suit that had been developed during the last ten years of deceleration by a team under the direction of Lydis. He had the toe of one heavy boot hooked under the horn of a cleat to check his outward drift, and his long-limbed body swiveled halfway around at the hips with a natural grace. He was not one of those people you saw bobbing around at the end of their safety ropes and having to haul themselves in.

“I agree. I have a computer working on an analysis of the curvatures to see what kind of a three-dimensional shape we can make them fit into. But clearly, we're looking at an artifact."

Artifact. Bram tasted the word with disbelief. From the size of the infrared emission shell, the unseen sun ought to have been a red giant—a swallower of solar systems. An artifact of that radius at the center of the Father World's system would have engulfed the two inner planets and the Father World itself.

“A trap around a star,” Bram said slowly. “A trap for energy. When we first began searching for an enclosed star radiating in the ten-micron part of the spectrum, I somehow visualized something like a sphere. I think we all did.” He paused to stare again at the distant wonder. “It's hard to imagine how any rectilinear material body the size of that could maintain its shape without gravitationally collapsing."

“There's only one answer, then. It's not straight."

Bram looked again, but the line was just as straight as before. “It's not?” he said.

“We're looking at the illuminated limb of another geometric form,” Jun Davd said. “One that can maintain its shape. I can think of at least two: a cylinder and—"

“Yes,” Bram breathed. “A disk. A spinning disk. Seen edge-on. But it's still unbelievable."

“We don't know what was possible to Original Man at the height of his glory. Perhaps, given another forty or fifty thousand years, the Nar might have learned how to utilize the total energy of a sun."

“Do you really think that's Man's sun in there?"

Jun Davd wrinkled his brow. “One of the suns he used, perhaps. The sun that gave him birth, no. I can't see him dismantling his own father world to make a beacon. There's nothing in this system larger than an asteroid. Nothing but a swarm of comets orbiting an invisible mass. And we're lucky he left us the comets."

He broke off to stare across the miles at the cagework trumpet bell of the ramscoop, which was no longer bathed in the spilled energies that had made it bright. A couple of comets had already been stuffed down its throat as start-up fuel for the next intersystem hop—the hop that the absence of worlds here had made unavoidable.

A space tug floated nearby, waiting to field the next slushball to be sent onward. Two tugs, actually, with a five-mile-wide net strung between them. It was the net that was visible as a fleck of light from a reflected spotlight beam. Bram wondered if his daughter Lydis was one of the pilots.

Closer at hand, against the fibrous wall of the root system across the way, a work crew was prying another ensnared comet away from Yggdrasil—a small one, less than a mile in diameter. With his magnification up, Bram could just make out the tiny space suited figures. They were melting away the clinging ice with dozens of two-man torches. It would require exquisite nicety of timing on the part of the foreman to make sure that the frozen sphere broke loose at just the right moment to cast it toward the waiting tugs instead of outward into the dark.

Yggdrasil could spare a few comets. Scores of the captured iceballs beaded the thirsty surface of its root hemisphere. The tree was working bravely to redistribute mass, but the unassimilated treasure trove still caused a wobble in the crown that took some getting used to. There was a lot of dropped glassware in the living quarters these days, but nobody was complaining. Abundance had returned to the tree after the long drought. The pools were filled, there was boating in the lagoon again, and water sports in the spherical pond at the center of the trunk. More important was the increase in metabolic products as Yggdrasil went through a growth spurt—sugars, starches, complex resins, and new cellulose for the factories.

Bram remembered the excitement when they had entered this queer, gutted system. Four previous ten-micron emission sources had proved to be false alarms—supergiants with circumstellar emission shells that were probably heated dust grains, not worth slowing down for. But the fifth candidate had shown all the symptoms of what the search team had jokingly taken to calling “Jao's shell."

It was Jao who first had proposed the theory of an enwrapped star whose output—by whatever unknown means—had been translated into the cosmos-spanning radio waves of Original Man's beacon.

“Where's all that building material going to come from?” Smeth had scoffed.

“From the dismantled planets,” Jao had replied. “And maybe they'd have to haul over the planets from a couple of nearby systems, too. They'd be turned into some kind of supermaterial made mostly of hydrogen, carbon, and oxygen—the atmospheres of a couple of gas giants mixed with the goodies at the core, and some cometary ice—you get the picture."

“How are you going to keep the shell from drifting off center?” Smeth had expostulated. “And if it rotates, how do you keep its substance from collecting at the equator?"

“Details,” Jao had replied airily. “We'll worry about them later. The main thing is to look for infrared sources that fit the basic picture."

The search area had been narrowed down to a sphere a thousand light-years in diameter. The Nar, long ago, had pinpointed an approximate location for Original Man's sun by analyzing wave fronts on a line stretched between the Father World and the new outpost on Juxt, and they had arrived at a value for the galactic year at that radius. Jun Davd, during the thirty-seven-million-year head-on approach to the Milky Way, had refined the figure still further. When the M supergiants and the small hot objects shining through dust had been eliminated, the number of candidates was small. Even so, it was surprising to have found it, apparently, on the first try.

“I calculate a total energy output for our invisible sun of four times ten to the thirty-third power ergs per second,” Jun Davd had announced shortly after Yggdrasil had settled into a cometary orbit. “That's based on the number of ergs per square inch falling on our collectors and applying the figure to an imaginary sphere at the radius of our own orbit. All in the deep infrared! It's consistent with the normal output at all wavelengths of a G-type dwarf similar to both Original Man's presumed sun and the Father World's primary. An attractive sun for our type of life, and the Nar's."

Jao had worked out approximate orbital periods for the first few comets Yggdrasil had chased. “Yah,” he'd said. “The comets are moving at the right speed for the postulated mass at the center. Maybe just a little bit high—but, like I said, the beacon builders might've dragged in an extra gas giant or two from another system."

It was going to be hard to pry Yggdrasil away from the comets after its long thirst. Bram—year-captain again for the fiftieth time—was under a lot of pressure to let the tree graze peaceably for a while in the outer reaches of the cometary halo. The human population of the living spaceship was now up to twenty-five thousand. It was getting a bit crowded along the axis of acceleration. The younger generation in particular had its eye on all the congenial real estate that would open up in the other branches if Yggdrasil went on permanent rotation mode.

But Bram did not dare give in. He had the feeling that if the populace spread out this time, he'd never get them back to the axis.

At Yggdrasil's leisurely rate of travel, it would take decades to drift from star to star—centuries or even millennia to search out the G-type dwarfs in this sector of the galaxy for the traces of Original Man. The new people did not have the same sense of urgency—the idea of a goal. For them, Yggdrasil was a way of life. It was more than possible than the citizenry could vote to settle in the first system that had rocky bodies to mine, a cometary shell to seed with a crop of more Yggdrasils.

Sometimes, on bad nights, Bram had a nightmare that he would never make planetfall again.

No, he thought. The only solution was to get his little convoy under fusion acceleration as quickly as possible, investigate the mystery at the heart of this system, then boost out again at one g.

Certain it was that Yggdrasil, left to its own devices, was not going to get much of an outward kick from the starlight to be found here!

Beside him, Jun Davd said, “I saw something just then."

Bram looked, but saw nothing except the faint scratch in the darkness and its attendant squiggles.

“Within the curve of the larger arc,” Jun Davd said.

Large, at this distance, meant nothing much more than a fairy's hangnail, even under full magnification, but Bram stared till his eyes watered.

Then he could just make it out—the dimmest of patches, like a foggy speck in his faceplate.

“It's leaking light,” Jun Davd said. “There are holes in it. That's diffuse reflection on a surface. Keep watching. And if I'm not mistaken..."

As if someone had punctured the fabric of space with a pin, a star peeped forth.

“It's not the whole star, of course,” Jun Davd mused. “It's probably the light from no more than ten or twenty percent of its surface to judge by the apparent magnitude. But we wouldn't have seen a disk, anyway, at this distance, just a point of light."

Bram didn't need a spectroscope to tell him what he was looking at. “It's a G-type sun,” he said.

“Yes, indeed,” Jun Davd said. “Well, we'd better uproot poor Yggdrasil again and go in for a closer look."

“It's embarrassing,” Ame said. “I have as many children as my great-great-great-grandmother."

She held up the twins for inspection, one in the crook of each arm. They were beginning to lose the wrinkled, recently boiled look, and it could be seen from their coloring and button features that they were going to take after Ame, not Smeth.

“Never mind, they're beautiful babies,” Mim said, nudging Bram in the ribs to keep him quiet. “And dizygotic twins are nobody's fault."

Smeth puttered nearby, a fatuous grin on his face. Ame's firm stewardship had done wonders for him; the rough edges, if not gone, were ground down a bit, and his friends pronounced him almost civilized. He and Ame had been together for ten Bobbings now. She teased him by telling him that it had simply become too much trouble keeping him at arm's length and that she had decided that maybe he was salvagable after all, despite five hundred years of bachelordom; to which he responded by swelling with pride and pleasure.

“I've used up my quota on my first try,” Ame said ruefully.

One child per century was the rule nowadays, enforced by society's unspoken displeasure. Those who had bred too thoughtlessly during the profligate days of middle-passage now sheepishly waited for the passing years to rehabilitate their reputations.

“You can have a share of mine or Lydis's,” Mim said. “We're not a prolific family. It all averages out."

“Yah, you want to talk embarrassed, look at Marg and Orris,” Jao said heartily. “Five children, like clockwork. Hey, I bet they have a cesium clock hanging over their sleeping nest so they can start working on number six the nanosecond it's licit."

“Jao, you're awful—stop that!” Ang exclaimed. “Excuse him, everybody."

“Why? What did I say?” Jao said innocently.

Bram, suppressing a smile, said to Ame, “Quotas may be a thing of the past sooner than you think. We ought to be ready to leave this system in a few years, and then it's just a question of time till we hit on a suitable planet."

He carefully refrained from specifying the father world of Original Man. He didn't want to appear to be too much of a visionary to these practical young people like Ame and her friends. It was generally accepted that there ought to be any number of suitable planets of G-type suns in Original Man's neck of the galaxy that once had been used by the vanished race and that therefore would possess breathable atmospheres and benign ecologies. Any sensible person aboard ought to be ready to settle for one of these. And any one of them would be a treasure trove for the paleontologists and the archeologists and the rest of the practitioners of the new theoretical sciences.

“Yah, as soon as your cohabitant here starts up the fusion engine, we'll be on our way,” Jao said. “How's it going, Smeth?"

Smeth, startled out of his slack-jawed adoration of his firstborn, replied, “I've got a crew aboard the probe overhauling the systems now. The four-wave mirrors need realignment, and there's been some minor damage to the web of the scoop, but it held up pretty well, considering. I'd say we ought to finish in a two of Tendays, and then we'll be ready to travel again."

“We ought to be able to land on the outside of whatever's walling off the sun!” Jao said enthusiastically. “The temperature's a nice comfortable three hundred degrees Absolute. Then we hightail it out of the system and start looking at yellow dwarfs. There's only eight or nine possibles within a twenty-light-year radius, and I'm betting one of them is the birthplace of Original Man. The stars around him would've had different relative motions—the guidepost constellations in the Message are no good to us now—but they'd have the same general orbits around the galactic center, and I'm betting they didn't drift too far apart. This beacon would've been one of the two or three closest.” He showed all this teeth to Ame in a gargantuan grin. “You'll be able to multiply with a clear conscience by the time the twins are grown."

Bram marveled that Jao was able to be so bluff and nonchalant on the subject in the face of his own tragedy. His second child, by some fluke, had proved to be immune to the immorality virus. The boy had grown into a humorous, likable chap with Jao's talent for physics. He had made some notable contributions and had left offspring himself before dying at the age of a hundred and thirty. That had been two centuries ago. Jao and Ang had never had another child after that.

Bram thought about his own new son, Edard. He and Mim had been lucky. Edard was a fine young man, still in his twenties but already making a contribution to human culture. From the first it had been evident that he had inherited Mim's musical talent. He had picked out tunes on the keyboard at the age of three, and by five he was well on the way to teaching himself to play Mim's cello, when Mim had taken a hand and started giving him formal lessons. Now, Edard was devoting himself to composition. He was obsessed by the six old symphonies that had been transmitted in score in the Message of Original Man and had applied himself to the task of recreating a live symphonic texture. He was probably the first composer in the history of the tree who was in a position to do so. With the increase in population, there were now enough first-rate players for an orchestra of thirty-eight people. They gave a concert every Tenday evening. Tonight they were going to introduce Edard's twenty-second symphony, the first in which he had totally abjured all electronic fill-ins for missing instruments and had limited himself to what the live players could produce. It promised to start a new, revolutionary trend.

Thinking of it reminded Bram to check his waistwatch for the time; the newer people might think him an old fuddy-duddy for clinging to habits learned on the Father World, but any honest person would have to admit that it was more polite to unobtrusively feel for the time with your fingertips than to read it off a visual wrist meter.

“We'd better think about going, Mim,” he said when he had a chance to get her attention. “It's only two hours till the concert."

Mim made the announcement general. “Sorry to rush off,” she said, “but I'm not cellist emeritus yet. I have to do my share with the others. Edard insists on a thick cello sound—he says he needs at least four."

“I'd better go, too,” Ang said. She was in the violin section. “No, you stay a while if you like,” she said to Jao.

“I wish I could hear the concert, Mim-tsu-mu," Ame said, “but I don't think I'd be welcome with two yowling babies."

“I'll stay with you,” Smeth said.

“No, you go,” Ame told him. “Don't you dare miss Edard's premiere."

“I can hear it later on tape,” he said.

“Tape?” Jao exploded. He put on an indignant expression for Mim's benefit. “Have you been paying the remotest attention to what Ang and Mim've been saying? The whole point is that it's living, breathing music. If you're going to hear it through a speaker; Edard might as well've done it all on a synthesizer!"

“Since when are you the great music lover?” Smeth snapped.

Ame stopped him with a look. “You go on,” she said. “One of us ought to be there.” She apologized to Mim. “Tell Edard-tsu-hsiung I'm sorry. I'll hear another performance of it.” The punctilious honorific she added to Edard's name meant something like “ancestor-brother.” Immortality was stretching the language out of shape.

The door rasp sounded. “I'll get it,” Smeth said, glad to escape.

While Mim and Ame said their good-byes, Bram heard raised voices at the door. Someone was wroth with Smeth. When leave-taking was done and Bram accompanied the two musicians to the entry chamber, he saw that the agitated caller was Jao's granddaughter, Enyd, the tree systems officer.

“I didn't expect to find you here, Captain,” Enyd said. “I came here to ask physics supervisor Smeth if it's true that he plans to put Yggdrasil under acceleration again, and if so to lodge a protest."

Smeth blustered, “The decision to reactive the drive is entirely the prerogative of—"

Bram cut him off. “Yes, it's true, Officer Enyd. I planned to discuss it with you first thing in the morning. I apologize for the fact that word apparently got to you in a roundabout way before I had that opportunity. You should have been the first to know."

“It was one of the technicians working on the overhaul,” Smeth fumed. “That loudmouth Perc, I'll bet. He must have spread it all over the place. All I did was to flash the workcage to ask how soon they could promise start-up if we decided to go! But I told them to keep their mouths shut."

“We'll have to make an announcement,” Bram said.

“Captain, Yggdrasil's barely had time to recover,” Enyd said. “It wants to spin normally for a while. It can't go back so soon to the artificial rhythm of adjusting its lateral growth once every Bobbing."

Bram looked at Mim. “Go on ahead, Mim. I'll catch up.” Mim and Ame left after a belated, perfunctory exchange of greetings with the distracted Enyd.

“How is Yggdrasil's ice reserve?” Bram asked, before Enyd could resume her complaints.

She hesitated, then said scrupulously, “Adequate, I suppose. But if we are to resume traveling, I would prefer to achieve satiety."

“I'll tell you what. When we get the fusion drive started, we'll chase down a few more comets for Yggdrasil before proceeding inward."

“Captain, water and trace elements aren't the only point. Yggdrasill needs a summer season, relief from stress, time for sustained photosynthesis. I wouldn't mind if you turned on the fusion fire for that; right now, Yggdrasil's trying to make do with starlight ... and the minor portion of infrared that it's able to convert into the six-hundred-sixty-and seven-hundred-thirty-millimicron range."

Her voice was almost tremulous, belying the cool, remote beauty that drove her suitors wild.

Bram spoke gravely. “I'm confident in your ability to monitor Yggdrasil's metabolism and do whatever is necessary, Chief Officer Enyd. I'm going to ask you to keep this tree happy for two more years. That's the time we'll need to penetrate to the center of this system under one gravity's acceleration. Then we can let Yggdrasil bask in the light of a real sun for a while, while we explore."

Edard sat in the cello section with Mim and the other two cellists, but sometimes in the finicky passages he would leave off playing and beat time for the other musicians. Bram watched the slender, dark-haired figure with pride. The music was first-rate; everybody said so, Mim had told him after the rehearsals. Even the old diehard, Kesper, had said with tears in his eyes, “If Mozart had written another symphony besides the Jupiter, it would have sounded like this!"

In the seat beside Bram, Smeth was trying to suppress a cough. Jao glared at him fiercely, and Smeth grumbled, “Where's the tune? Everybody's playing something different."

There were whispers of "Quiet!" from the surrounding seats, and Smeth subsided. Bram looked around the great, carved wooden chamber. Every one of the eight thousand seats was filled, and a repeat performance had been scheduled for those who were unable to get in. Edard had refused to allow a microphone pickup, saying that it would only encourage people to listen in their own chambers.

The live sound was glorious, Bram had to admit. The acoustics of the wooden cavity, refined over the centuries, helped.

Stringed instruments had come a long way in five hundred years. The new cello was like a truncated pyramid the height of a child, and the performers played it vertically instead of horizontally on a stand, as before. The bow weighed only a couple of pounds now and could be played without an elbow clamp; it was a lightweight plastic framework with its own power source to keep the continuous friction band running smoothly around its sprockets. Mim was a stickler for proper bow technique. She told her students that the bow should hardly be moved at all—just raised or lowered on the eight strings.

The music was coming to a climax. The cellos all buzzed in unison; the violins soared; the horn players raised their long, conical instruments and blared in thrilling harmony.

It was over. Bram stood with the rest and applauded. On the central platform, Edard looked flushed and pleased. Mim went over and kissed him.

“You've got a talented boy, all right,” Jao said. “Too bad he has no head for science."

Bram laughed. “Are you trying to sound like Smeth?"

“I'd never say a thing like that,” Smeth protested indignantly. “I thought it was ... very good."

The applause rose, swelled. The other musicians were closing around Edard, clapping him on the back, grasping his hands. Edard looked no younger than the others, but Bram could not help reflecting on his age. What will he develop into, he thought, with all eternity ahead of him?

The audience had settled down again for the encore. Edard had wisely refrained from repeating his own music and was giving them the familiar slow movement of the Jupiter Symphony—deliberately inviting comparison, Bram thought, smiling at the arrogance of youth. He closed his eyes and listened as the long-drawn cello melody gravely climbed its steps while the violins scolded it. The audience held its breath. Even Smeth sat rapt and silent beside him.

There was a tap on his shoulder, and he turned toward the aisle to find Trist leaning apologetically toward him.

“I'm sorry,” Trist whispered, “but something's come up. I think you'd better have a look at it. Jun Davd's waiting for us."

The violins had succeeded in wresting the theme back from the cellos. Bram looked longingly at the communing musicians on the platform. Mim and Edard would expect to see him backstage afterward. He gave a resigned shrug and eased his way out while people glared at him. He followed Trist up the aisle. The heavenly music floated after him. A backward glance had told him that Jao was trailing along behind, prodding a resisting Smeth.

“Now, what's this about?” Bram said when they were out of the hall.

“We're getting some very strange radio signals,” Trist said.

Bram stopped in his tracks. Smeth and Jao piled into him. “Intelligent?” he said.

“Let's just say they're nonnatural,” Trist said.

Jao's big hand grabbed Trist by the shoulder and spun him around. “Where are they coming from?” he said hoarsely.

“From everywhere,” Trist said.

“What do you mean?” Bram said.

Trist bit his lip. “I mean from half the sky. From every star in a volume of space that—” He broke off. “Best come see for yourself."

“But what kind of—"

“Jun Davd's still sorting out the data the computer dumped,” Trist said. “He'll probably have a simulation ready by the time we get there."

And that was all they could get out of him during the trip to the Message center. It was a ride of over twenty minutes, even on the high-speed mag-lev tubeway that had finally replaced the outside slingshot pods on eight of the twelve major branches. Bram had to watch Smeth fidget and listen to Jao grumble all the way. He found it hard to contain his own curiosity, but he knew there was no point in pressing Trist.

The Message center had been gathering dust during the five centuries of coasting between galaxies, and had been reopened only in recent years, as an adjunct of the observatory. It had been thought worthwhile to begin searching for possible evidence of artificial signals as they approached the volume of space that once had held the civilization of Original Man—if they were going to have intelligent neighbors, they had better know about it—and the radio installation still held a lot of specialized equipment and the old programs that Trist had used in monitoring the Nar wavelengths on the way out of the Whirlpool galaxy. But the search program still took a back seat to the long-range radioastronomy programs that Jun Davd had set up using the Message center's antenna ray, including the accreting computer model of Jao's magnetic eight-spoke theory to account for the periodic extinctions of Earth's life.

The tremendous cylindrical arcade was darkened and silent as they floated through it; with the fusion drive turned off, the tree was practicing a few small economies in its use of electric power. Far down an avenue of shadowy capacitors, Bram could see the bobbing lights of one of the skeleton maintenance crews that made periodic inspection tours here. Trist led the way in a series of shallow touchdowns. The gravity was almost nil this close to the tree's center of rotation; they had to wait once for Smeth, who incautiously bounced too high and got himself captured by what had been the ceiling when the tree had been under acceleration.

“Here we are,” Trist said, letting them into his old office.

Jun Davd looked up at them from a jumble of printouts and scrawled summaries spread out around him on a variety of work surfaces. Screens and variously organized date windows were fine, but there was nothing like paper when you wanted to see everything at once.

“Ah, here you are,” he said. “Did you tell them?"

“Yes,” Trist said.

“Tell us?” Jao roared. “He told us nothing except that we'd better come have a look for ourselves."

Jun Davd said imperturbably, “You know that we have a number of ingenious computer programs written by Trist, designed to search likely wavelengths for patterns of various types, with all sorts of Doppler compensations—for our motion, the motion of stars, the motions of presumed planets orbiting in a variety of presumed planes, shifts in limb brightness along the edges of the presumed planets as the planets themselves rotate around an infinite number of presumed axes ... it's all very complicated, particularly when we ourselves are moving."

“Yes, yes,” Jao said impatiently.

“Some of the data goes back over a year—we'd already spotted the infrared emission of our invisible star and were decelerating toward it. But the computer never sounded the alarm. Neither did the technicians who conducted the occasional random sampling. But that's not surprising. The data picture didn't become really interesting till we came to rest."

Seeing Jao redden toward explosion, Bram said. “Take pity on the man, Jun Davd."

“Here it is translated into audio,” Jun Davd said. “With a little guesswork, of course."

He flipped a switch, and the room was suddenly filled with clicks and snaps, as if a million demented children were all breaking twigs at once.

Bram felt ice down his spine. “What is it?” he said.

“It has no information-bearing content that we can see. On the other hand we can't make it correspond to any natural radio phenomenon that we can imagine."

Trist broke in. “So we decided it must be a by-product of some artificial process. Like back-lobe leakage from the space-based antennas of solar power satellites."

“Then an analysis of the wave forms suggested strongly that the clicks were acoustic in nature,” Jun Davd said. “So we discarded the idea that they were some kind of static, either natural or artificial."

Bram listened to the hard, dry snapping sounds for a moment. Regarded as actual physical noises, they were even more puzzling. “They'd have to be produced in a medium: solid, liquid, or gas,” he said.

“Ridiculous,” Smeth said. “There must be a natural explanation. Remember how pulsars fooled the early radio astronomers? It's some property of the stars in this arm of the galaxy."

Bram frowned. “Trist said that the signals come from everywhere. From the invisible star we're orbiting too?"

“No. Everywhere but,” Trist volunteered.

“Now we come to the interesting part,” Jun Davd said. “Bear with me a moment. This is still very crude. But it will give you an idea."

He fiddled with a console, and a holographic window lit up in the display board. It was a three-dimensional star map, reasonably realistic, with points of colored light scattered through the velvet darkness. A dull red bead began winking in a lower corner.

“That's our position,” Jun Davd said. “Or the position of our infrared star. We're somewhere in the cometary belt—we won't quibble about half a light-year or so. And now here's the route we took from the center of the galaxy."

A yellow dotted line grew from the blinking bead, angling inward in the holographic illusion, and disappeared behind the windowframe on the opposite side.

“Now, all of this space is filled with these odd radio emissions—they've all had different times of origin and the oldest of them are presumably spreading in spheres many hundreds of light-years in diameter. Far beyond the boundaries of my little map. But that's not what we're concerned with. We want to show the stars of origin."

He fiddled with the console again, and a whole swarm of stars in the center of the holo image began blinking. The swarm was in the shape of a lumpy sphere—as near to a perfect sphere as the actual distribution of stars in space could make it.

With one exception. There was a curiously flat, squashed area on the part of the sphere directly opposite the bead representing the infrared star, which hung just outside the boundary of winking stars.

“I don't think that part of the sphere is actually flattened,” Jun Davd said. “That's about forty light-years away—at the furthest distance from us. I think any emissions originating there have started fairly recently and simply haven't reached us yet."

Trist nodded in agreement. “Yes, we intersected a small chord of this ... spherical volume of space on our way here, and when we crank back the data we find that we've witnessed several discrete jumps in the size of the globe. It seems to be growing quite uniformly, at about one-tenth of the speed of light."

Jun Davd's fingers flicked buttons, and a star at the surface of the shell sent a spray of three dotted lines toward the line embedded within the sphere that represented Yggdrasil's route, making an equilateral triangle bisected at the vertex. He added three little green Yggdrasils where the dotted lines met the route.

“No reception,” Jun Davd said, tapping the first Yggdrasil at the earliest position on the route. He went on to tap the second Yggdrasil, where the bisecting line showed the shortest distance to the star. “First reception,” he said. Then he pointed to the third little tree symbol. “And we're still receiving at the same radial distance as the previous no-reception zone, so knowing our speed and the distance covered, and throwing in a little Doppler anaylsis of about a dozen similar cases, we get a pretty good value for the rate of growth of the shell."

“And virtually every single star within the shell is giving off radio clicks,” Trist said.

The other three looked at one another. The thought was inescapable. “Original Man?” Bram said.

“No, impossible!” Jao said.

Smeth was getting excited. Too excited. “Why are we wasting time here?" he said. “Whatever this phenomenon is, it's growing from a center.” He squinted at the pinch of stars in the middle of the representation—a couple of yellow dwarfs, one with a smaller orange star and a red dwarf for companions; a solitary red dwarf; a blue-white giant attended by a burnt-out cinder. “Let's investigate the center of the sphere and see if we can find out what's causing it!"

Jao bellowed in outrage. He could see his lovely enclosed star slipping away from him. “What? That's twenty light-years away! You're talking seven, eight years of ship time by the time we build up enough gamma at one g! We're here now! We can be at the center of this system in less than two years!"

Jun Davd was no help. He stood there smiling. Bram turned to Trist. “How fast did you say that sphere of clicking stars is growing? At about one-tenth the speed of light?"

“That's right,” Trist said.

Bram exercised his prerogatives as year-captain. “In that case we can stay here and wait for it. This star is due to give off clicks any time now."