"Your name will be famous in the history of astronomy forever."

"Or infamous," he said balefully.

"Athor, I don't understand what you-"

"Let me be, Nyilda. I'm not going to keel over at my desk, believe me. I feel rejuvenated by what I'm doing here. And it's work that only I can do. If that sounds pigheaded, so be it, but it's absolutely essential that I-"

She sighed. "Yes, of course. But don't overdo it, Athor. That's all I ask."

Was he overdoing it? he wondered now. Yes, yes, of course he was. There wasn't any other way. You couldn't dabble in these matters. You had to throw yourself wholeheartedly into them. When he was working out Universal Gravitation he had worked sixteen-, eighteen-, twenty-hour days for weeks on end, sleeping only when sleep became unavoidable, snatching brief naps and awakening ready and eager for work, with his mind still bubbling with the equations he had left unfinished a little while before.

But he had been only thirty-five or so, then. He was nearly seventy now. There was no denying the inroads of age. His head ached, his throat was dry, there was a nasty pounding in his chest. Despite the warmth of his office his fingertips were chilly with weariness. His knees were throbbing. Every part of his body protested the strain he had been putting on it.

Just a little while longer today, he promised himself, and then I'll go home.

Just a little while longer.

Postulate Eight- "Sir?"

"What is it?" he asked.

But his voice must have turned the question into some sort of fierce snarl, for when he glanced around he saw young Yimot standing in the doorway doing a bizarre series of wild twitches and convulsions, as though he were dancing on hot embers. There was terror in the boy's eyes. Of course Yimot always seemed intimidated by the Observatory director-everybody around here was, not just graduate students, and Athor was used to it. Athor was awesome and he knew it. But this went beyond the ordinary. Yimot was gazing at him in undisguised fear mingled with what seemed like astonishment.

Yimot struggled visibly to find his voice and said huskily, "The calculations you wanted, sir-"

"Oh. Yes. Yes. Here, give me."

Athor's hand was trembling violently as he reached for the printouts Yimot had brought him. Both of them stared at it, aghast. The long bony fingers were pale as death and they were quivering with a vehemence that not even Yimot, famed for his remarkable nervous reactions, could have equaled. Athor willed his hand to be still, but it would not. He might just as well have been willing Onos to spin backward across the sky.

With an effort he snatched the papers from Yimot and slapped them down on the desk.

Yimot said, "If there's anything I can get you, sir-"

"Medication, you mean? How dare you suggest-"

"I just meant something to eat, or maybe a cold drink," Yimot said in a barely audible whisper. He backed slowly away as if expecting Athor to growl and leap for his throat.

"Ah. Ah. I see. No, I'm fine, Yimot. Fine!"

"Yes, sir."

The student went out. Athor closed his eyes a moment, took three or four deep breaths, struggled to calm himself. He was near the end of his task, of that he was sure. These figures that he had asked Yimot to work out for him were almost certainly the last confirmation he needed. But the question now was whether the work was going to finish him before he finished the work.

He looked at Yimot's numbers.

Three screens sat before him on his desk. On the left-hand one was the orbit of Kalgash as calculated according to conventional reckoning under the Theory of Universal Gravitation, outlined in blazing red. On the right-hand screen, in fiery yellow, was the revised orbit that Beenay had produced, using the new university computer and the most recent observations of Kalgash's actual position. The middle screen carried both orbits plotted one over the other. In the past five days Athor had produced seven different postulates to account for the deviation between the theoretical orbit and the observed one, and he could call up any of those seven postulates on the middle screen with a single key-stroke.

The trouble was that all seven of them were nonsense, and he knew it. Each one had a fatal flaw at its heart-an assumption that was there not because the calculations justified it, but only because the situation called for some such sort of special assumption in order to make the numbers turn out the right way. Nothing was provable, nothing was confirmable. It was as though in each case he had simply decreed, at some point in the chain of logic, that a fairy godmother would step in and adjust the gravitational interactions to account for the deviation. In truth that was precisely what Athor knew he needed to find. But it had to be a real fairy godmother. Postulate Eight, now- He began keying in Yimot's calculations. Several times his trembling fingers betrayed him and he made an error; but his mind was still sharp enough to tell him instantly that he had hit the wrong key, and he backed up and repaired the damage each time. Twice, as he worked, he nearly blacked out from the intensity of his effort. But he forced himself to go on.

You are the only person in the world who can possibly do this, he told himself as he worked. And so you must.

It sounded foolish to him, and madly egocentric, and perhaps a little insane. It probably wasn't even true. But at this stage in his exhaustion he couldn't allow himself to consider any other premise but that of his own indispensability. All the basic concepts of this project were held in his mind, and his mind alone. He had to push himself onward until he had closed the last link in the chain. Until-

There.

The last of Yimot's numbers went into the computer.

Athor hit the key that brought the two orbits up into view simultaneously on the middle screen, and hit the key that integrated the new number with the existing patterns.

The brilliant red ellipse that was the original theoretical orbit wavered and shifted, and suddenly it was gone. So was the yellow one of the observed orbit. Now there was only a single line on the screen, a deep, intense orange, the two orbital simulations overlapping to the last decimal place.

Athor gasped. For a long moment he studied the screen, and then he closed his eyes again and bowed his head against the edge of the desk. The orange ellipse blazed like a ring of flame against his closed eyelids.

He felt a curious sense of exultation mixed with dismay.

He had his answer, now; he had a hypothesis that he was certain would stand up to the closest scrutiny. The Theory of Universal Gravitation was valid after all: the epochal chain of reasoning on which his fame was based would not be overthrown.

But at the same time he knew now that the model of the solar system with which he was so familiar was in fact erroneous. The unknown factor for which they had sought, the invisible giant, the dragon in the sky, was real. Athor found that profoundly upsetting, even if it bad rescued his famous theory. He had thought for years that he fully understood the rhythm of the heavens, and now it was clear to him that his knowledge had been incomplete, that a great strangeness existed in the midst of the known universe, that things were not as he had always believed them to be. It was hard, at his age, to swallow that.

After a time Athor looked up. Nothing had changed on the screen. He punched in a few interrogative equations, and still nothing changed. He saw one orbit, not two.

Very well, he told himself. So the universe is not quite as you thought it was. You 'd better rearrange your beliefs, then. Because you certainly can't rearrange the universe.

"Yimot!" he called. "Faro! Beenay! All of you!"

Roly-poly little Faro was the first through the door, with beanpole Yimot just behind him, and then the rest of the Astronomy Department, Beenay, Thilanda, Klet, Simbron, and some others. They clustered just inside the entrance to his office. Athor saw by the expression of shock on their faces that he must be a frightful sight indeed, no doubt wild and haggard, his white hair standing out in all directions, his face pale, his whole appearance that of an old man right on the edge of collapse.

It was important to defuse their fears right away. This was no moment for melodrama.

Quietly he said, "Yes, I'm very tired and I know it. And I probably look like some demon out of the nether realms. But I've got something here that looks like it works."

"The gravitational lens idea?" Beenay said.

"The gravitational lens is a completely hopeless concept," Athor said frostily. "The same with the burned-out sun, the fold in space, the zone of negative mass, and the other fantastical notions we've been playing with all week. They're all very pretty ideas but they don't stand up to hard scrutiny. There is one that does, though."

He watched their eyes widen.

Turning to the screen, he began once again to set up the numbers of Postulate Eight. His weariness dropped away as he worked: he struck no wrong keys this time, he felt no aches and pains. He had moved into a realm beyond fatigue.

"In this postulate we assume," he said, "a non-luminous planetary body similar to Kalgash, which is in orbit not around Onos but around Kalgash itself. Its mass is considerable, in fact is nearly the same as that of Kalgash itself: sufficient to exert a gravitational force on our world that causes the perturbations of our orbit which Beenay has called to our attention."

Athor keyed in the visuals and the solar system appeared on the screen in stylized form: the six suns, Kalgash, and the postulated satellite of Kalgash.

He turned back to face the others. They were all looking at each other uneasily. Though they were half his age, or even less, they must be having as much trouble coming to an intellectual and emotional acceptance of the whole idea of another major heavenly body in the universe as he had had. Or else they simply must think he had become senile, and somehow had slipped up in his calculations.

"The numbers supporting Postulate Eight are correct," Athor said. "I pledge you that. And the postulate has withstood every test I could apply."

He glared at them defiantly, looking ferociously at each of them in turn, as if to remind them that he wa~ the Athor 77 who had given the world the Theory of Universal Gravitation, and that he had not yet taken leave of his faculties.

Beenay said softly, "And the reason why we are unable to see this satellite, sir-?"

"Two reasons," replied Athor serenely. "Like Kalgash itself, this planetary body would shine only by reflected light. If we assume that its surface is made up largely of bluish rock-not an implausible geological likelihood-then the light reflected from it would be positioned along the spectrum in such a way that the eternal blaze of the six suns, combined with the lightscattering properties of our own atmosphere, would completely mask its presence. In a sky where several suns are shining at virtually every moment, such a satellite would be invisible to us."

Faro said, "Provided the orbit of the satellite is an extremely large one, isn't that so, sir?"

"Right." Athor keyed in the second visual. "Here's a closer look. As you see, our unknown and invisible satellite travels around us on an enormous ellipse that carries it extremely far from us for many years at a time. Not so distant that we don't display the orbital effects of its presence in the heavens-but far enough so that ordinarily there is no possibility of our getting a naked-eye view of this dim rocky mass in the sky, and very little possibility of our discovering it even with our telescopes. Since we have no way of knowing it's there by ordinary observation, it would be only by the wildest chance that we'd have detected it astronomically."

"But of course we can go looking for it now," said Thilanda 191, whose specialty was astrophotography.

"And of course we will," Athor told her. They were coming around to the idea now, he saw. Every one of them. He knew them well enough to see that there were no secret scoffers. "Though you may find the search harder than you suspect, very definitely a needle-in-a-haystack proposition. But there'll be an immediate appropriation for the work, that I pledge you."

Beenay said, "One question, sir."

"Go on."

"If the orbit's as eccentric as your postulate supposes, and therefore this satellite of ours, this-Kalgash Two, let's call it for the moment-Kalgash Two is extremely distant from us during certain parts of its orbital cycle, then it stands to reason that at other parts of its cycle it's bound to move into a position that's very much closer to us. There has to be some range of variation even in the most perfect orbit, and a satellite traveling in a large elliptical orbit is likely to have an extreme range between the farthest and the closest points of approach to the primary."

"That would be logical, yes," Athor said.

"But then, sir," Beenay went on, "if we assume that Kalgash Two has been so far from us during the entire period of modern astronomical science that we've been unable to discover its very existence except by the indirect means of measuring its effect on our own world's orbit, wouldn't you agree that it's probably coming back from its farthest distance right now? That it must currently be approaching us?"

"That doesn't necessarily follow," Yimot said, with a great flurry of his arms. "We don't have any idea where it is along its orbital path right now, or how long it takes to make one complete circuit around Kalgash. It might be a ten-thousand-year orbit and Kalgash Two could still be heading away from us after an approach in prehistoric times that no one remembers."

"True," Beenay admitted. "We can't really say whether it's coming or going at the present moment. Not yet, anyway."

"But we can try to find out," Faro said. "Thilanda has the right idea. Even though all the numbers check out, we need to see whether Kalgash Two is actually out there. Once we find it we can begin to calculate its orbit."

"We should be able to calculate its orbit simply from the perturbations it causes in ours," said Klet, who was the department's best mathematician.

"Yes," Simbron put in-she was a cosmographer-"and we can also figure out whether it's approaching or heading away from us. Gods! What if it's heading this way? What an amazing event that would be! A dark planetary body cutting across the sky-passing between us and the suns! Possibly even blotting out the light of some of them for a couple of hours!"

"How strange that would be," Beenay mused. "An eclipse, I suppose you could call it. You know: the visuaYeffect that occurs when some object gets between a viewer and the thing he's looking at. But could it happen? The suns are so huge- how could Kalgash Two actually conceal one of them from view?"

"If it came close enough to us it might," Faro said. "Why, I could imagine a situation in which-"

"Yes, work out all possible scenarios, why don't you?" Athor interjected suddenly, cutting Faro off with such brutal abruptness that everyone in the room turned to stare at him. "Play with the idea, all of you. Push it this way and that, and see what you get."

Suddenly he couldn't bear to sit here any longer. He had to get away.

The exhilaration he had felt since putting the last piece into place had abruptly deserted him. He felt a terrible leaden weariness, as though he were a thousand years old. Chills were running along his arms down into his fingers, and something was squirming frantically in the muscles of his back. He knew that he had pushed himself beyond all endurance now. It was time for younger workers to relieve him of this enterprise.

Rising from his chair before the screens, Athor took one uncertain reeling step toward the middle of the room, recovered himself before he could stumble, and walked slowly and with all the dignity he could muster past the Observatory staff. "I'm going home," he said. "I could use some sleep."

Beenay said, "Am I to understand that the village was destroyed by fire nine times in a row, Siferra? And they rebuilt it every time?"

"My colleague Balik thinks there may be only seven villages piled up in the Hill of Thombo," the archaeologist replied.

"And he may be right, actually. Things are pretty jumbled down toward the lowest levels. But seven villages, nine villages-no matter how many it is exactly, it doesn't change the fundamental concept. Here: look at these charts. I've worked them up from my excavation notes. Of course what we did was just a preliminary dig, a quick slice through the whole hill, with the really meticulous work left for a later expedition. We discovered the hill too late in our work to do anything else. But these charts'll give you an idea. -You aren't going to be bored, are you? All this stuff does interest you, doesn't it, Beenay?"

"I find it completely fascinating. Do you think I'm so totally preoccupied with astronomy that I can't pay attention to any of the other disciplines? -Besides, archaeology and astronomy sometimes go hand in hand. We've learned more than a little about the movements of the suns through the heavens by studying the ancient astronomical monuments that you people have been digging up here and there around the world. Here, let me see."

They were in Siferra's office. She had asked Beenay to come there to discuss a problem which she said had unexpectedly arisen in the course of her research. Which puzzled him, because he didn't immediately see how an astronomer could help an archaeologist in her work, despite what he had just said about archaeology and astronomy sometimes going hand in hand. But he was always glad to have a chance to visit with Siferra.

They had met initially five years before, when they were working together on an interdisciplinary faculty committee that was planning the expansion of the university library. Though Siferra had been out of the country most of the time since then doing field work, she and Beenay did enjoy meeting for lunch now and then when she was there. He found her challenging, highly intelligent, and abrasive in a refreshing sort of way. What she saw in him he had no idea: perhaps just an intellectually stimulating young man who wasn't involved in the poisonous rivalries and feuds of her own field and had no apparent designs on her body.

Siferra unfolded the charts, huge sheets of thin parchmentlike paper on which complex, elegant diagrams had been ruled with pencil, and she and Beenay bent forward to examine them at close range.

He had been telling the truth when he said he was fascinated by archaeology. Ever since he'd been a boy, he had enjoyed reading the narratives of the great explorers of afitiquity, such men as Marpin, Shelbik, and of course Galdo 221. He found the remote past nearly as exciting to think about as the remote reaches of interstellar space.

His contract-mate Raissta wasn't greatly pleased by his friendship with Siferra. She had rather testily implied, a couple of times, that it was Siferra herself who fascinated him, not her field of research. But Beenay thought Raissta's jealousy was absurd. Certainly Siferra was an attractive woman-it would be disingenuous to pretend otherwise-but she was relentlessly non-romantic and every man on campus knew it. Besides, she was something like ten years older than Beenay. Handsome as she was, Beenay had never thought of her with any sort of intimate intentions.

"What we have here, first, is a cross section of the entire hill," Siferra told him. "I've plotted each separate level of occupation in a schematic way. The newest settlement's at the top, naturally-huge stone walls, what we call the cyclopean style of architecture, typical of the Beklimot culture in its mature period of development. This line here in the level of the cyclopean walls represents a layer of charcoal remains-enough charcoal to indicate a widespread conflagration that must have utterly wiped the city out. And here, below the cyclopean level and the burn line, is the next oldest settlement."

"Which is constructed in a different style."

"Exactly. You see how I've drawn the stones of the walls? It's what we call the crosshatch style, characteristic of the early Beklimot culture, or perhaps the culture that developed into Beklimot. Both these styles can be seen in the Beklimot-era ruins that surround the Hill of Thombo. The main ruins are cyclopean, and here and there we've found a little crosshatch stuff, just a mere outcropping or two, which we call protoBeklimot. Now, look here, at the border between the crosshatch settlement and the cyclopean ruins above it."

"Another fire line?" Beenay said.

"Another fire line, yes. What we have in this hill is like a sandwich-a layer of human occupation, a layer of charcoal, another layer of human occupation, another layer of charcoal. So what I think happened is something like this. During the time of the crosshatch people there was a devastating fire that scorched a pretty good chunk of the Sagikan Peninsula and forced the abandonment of the Thombo village and other crosshatch-style villages nearby. Afterward, when the inhabitants came back and began to rebuild, they used a brand-new and more elaborate architectural style, which we call cyclopean because of the huge building-stones. But then came another fire and wiped out the cyclopean settlement. At that point the people of the area gave up trying to build cities on the Hill of Thombo and this time when they rebuilt they chose another site nearby, which we term Beklimot Major. We've believed for a long time that Beklimot Major was the first true human city, emerging from the smaller crosshatch-type proto-Beklimotperiod settlements scattered all around it. What Thombo tells us is that there was at least one important cyclopean city in the area before Beklimot Major existed."

"And the Beklimot Major site," Beenay said, "shows no trace of fire damage?"

"No. So it wasn't there when the city on top of Thombo was burned. Eventually the whole Beklimot culture collapsed and Beklimot Major itself was abandoned, but that was for other reasons having to do with climatic shifts. Fire had nothing to do with it. That was perhaps a thousand years ago. But the fire that wrecked the topmost Thombo village seems to have been much earlier than that. I'd guess about a thousand years earlier. The radiocarbon dates from the charcoal samples will give us a more precise figure when we get them from the lab."

"And the crosshatch settlement-how old is that?"

"Orthodox archaeological belief has been that the fragmentary crosshatch structures we've found here and there on the Sagikan Peninsula are only a few generations older than the Beklimot Major site. After the Thombo excavation, I don't think so. My guess is that the crosshatch settlement on that hill is two thousand years older than the cyclopean buildings on top of it."

"Two thousand-? And you say there are other settlements below that one?"

"Look at the chart," Siferra said. "Here's number three-a kind of architecture we've never seen before, nothing at all like crosshatch work. Then another burn line. Settlement number four. And a burn line. Number five. A burn line. Then numbers six, seven, eight, and nine-or, if Balik's reading is correct, just numbers six and seven."

"And each one destroyed by a great fire! That seems pretty remarkable to me. A deadly cycle of destruction, striking again and again and again in the same place."

"The remarkable thing," said Siferra in a curiously somber tone, "is that each of these settlements appears to have flourished for approximately the same length of time before being destroyed by fire. The layers of occupation are quite extraordinarily similar in thickness. We're still waiting for the lab reports, you understand. But I don't think my eyeball estimate is very far off. And Balik's figures are the same as mine. Unless we're completely mistaken, we're looking at a minimum of fourteen thousand years of prehistory in the Hill of Thombo. And during those fourteen thousand years the hill was periodically swept by massive fires that forced its abandonment with clockwork regularity-one fire every two thousand years, just about exactly!"

"What?"

A shiver traveled along Beenay's spine. His mind was beginning to leap to all manner of improbable and disturbing conclusions.

"Wait," Siferra said. "There's more."

She opened a drawer and took out a stack of glossy photographs.

"These are pictures of the Thombo tablets. Mudrin 505 has the originals-the paleographer, you know. He's been trying to decipher them. They're made of baked clay. We found these three in Level Three, and these in Level Five. They're both written in extremely primitive scripts, and the writing on the older ones is so ancient that Mudrin can't even make a start on them. But he's been able very tentatively to puzzle out a couple of dozen words from the Level Three tablets, which are written in an early form of the Beklimot script. So far as he can tell at this point, they're an account of the destruction of a city by fire-the work of angry gods who periodically find it necessary to punish mankind for wickedness."

"Periodically?"

"That's right. Does it begin to sound familiar?"

"The Apostles of Flame! My God, Siferra, what have you stumbled on here?"

"That's what I've been asking myself since Mudrin brought me the first sketchy translations." The archaeologist swung around to face Beenay, and for the first time Beenay saw how bleary her eyes were, how tense and drawn her face. She looked almost distraught. "Do you see now why I asked you to come here? I can't talk about this with anyone in the department. Beenay, what am I going to do? If any of this becomes public, Mondior 71 and his whole crazy crew will proclaim it from the rooftops that I've discovered firm archaeological proof of their crackpot theories!"

"You think so?"

"What else?" Siferra tapped the charts. "Here's evidence of repeated fiery destruction at two-thousand-year intervals, roughly, over a period of many thousands of years. And these tablets-the way it looks now, they might actually be some sort of prehistoric version of the Book of Revelations. Taken together, they provide, if not actual confirmation of the rantings of the Apostles, then at least a solid rational underpinning for their whole mythology."

"But repeated fires at a single site don't prove that there was worldwide devastation," Beenay objected.

"It's the periodicity that worries me," said Siferra. "It's too neat, and too close to what Mondior's been saying. I've been looking at the Book of Revelations. The Sagikan Peninsula is a holy place to the Apostles, did you know that? The sacred site where the gods formerly made themselves visible to humanity, so they say. And therefore it stands to reason-listen to me, it stands to reason," she said, laughing bitterly-"that the gods would preserve Sagikan as a warning to mankind of the doom that will come again and again if we don't alter our wicked ways."

Beenay stared at her, stunned.

He knew very little about the Apostles and their teachings, really. Such pathological fantasizing had never held any interest for him, and he had been too busy with his scientific work to pay heed to Mondior's windy apocalyptic prophecies.

But now the memory of the conversation he had had some weeks before with Theremon 762 at the Six Suns Club burst with furious impact into his consciousness. ". . ~. won't be the first time the world has been destroyed . . . the gods have deliberately made mankind imperfect and given us a single year-one of their divine years, not one of our little ones-in which to shape up. That's called a Year of Godliness, and it '~c exactly two thousand and forty-nine of our years long."

No. No. No. No. Idiocy! Claptrap! Hysterical folly!

There was more. "Again and again, when the Year of Godliness has ended, the gods have discovered that we're still wicked and sinful, and so they have destroyed the world by sending down heavenly flames. . . . So say the Apostles, anyway."

No! No!

"Beenay?" Siferra said. "Are you all right?"

"Just thinking," he told her. "By Darkness, it's true! You'd give the Apostles complete confirmation!"

"Not necessarily. It would still be possible for people who are capable of thinking clearly to reject Mondior's ideas. The destruction of Thombo by fire-even the repeated destruction of Thombo at apparently regular intervals of approximately two thousand years-doesn't in any way prove that the whole world was destroyed by fire. Or that some such great fire must inevitably come again. Why should the past necessarily be recapitulated in the future? But people who are capable of thinking clearly are in a minority, of course. The rest of them will be swayed by Mondior's use of my findings and go into an immediate panic. You know, don't you, that the Apostles claim the next great world-destroying fire is due to strike us next year?"

"Yes," Beenay said hoarsely. "Theremon tells me that they've pinpointed the exact day. It's a two-thousand-andforty-nine-year cycle, actually, and this is the two-thousandand-forty-eighth year, and in something like eleven or twelve more months, if you believe Mondior, the sky will turn black and fire will descend on us. I think the nineteenth of Theptar is when it's supposed to happen."

"Theremon? The newspaperman?"