“Mendez?” said the young man in the blue-and-green tartan jacket. “Why, yes ... sure I’ve heard of it. Why?”

The clerk behind the desk looked again at the information screen. “That’s the destination we have on file for Scholar Duckworth, Mr. Turnbull. That was six months ago.” He looked up from the screen, waiting to see if Turnbull had any more questions.

Turnbull tapped his teeth with a thumbnail for a couple of seconds, then shrugged slightly. “Any address given for him?”

“Yes, sir. The Hotel Byron, Landing City, Mendez.”

Turnbull nodded. “How much is the fare to Mendez?”

The clerk thumbed a button which wiped the information screen clean, then replaced it with another list, which flowed upward for a few seconds, then stopped. “Seven hundred and eighty-five fifty, sir,” said the clerk. “Shall I make you out a ticket?”

Turnbull hesitated. “What’s the route?”

The clerk touched another control, and again the information on the screen changed. “You’ll take the regular shuttle from here to Luna, then take either the Stellar Queen or the Oriona to Sirius VI. From there, you will have to pick up a ship to the Central Worlds--either to Vanderlin or BenAbram--and take a ship from there to Mendez. Not complicated, really. The whole trip won’t take you more than three weeks, including stopovers.”

“I see,” said Turnbull. “I haven’t made up my mind yet. I’ll let you know.”

“Very well, sir. The Stellar Queen leaves on Wednesdays and the Oriona on Saturdays. We’ll need three days’ notice.”

Turnbull thanked the clerk and headed toward the big doors that led out of Long Island Terminal, threading his way through the little clumps of people that milled around inside the big waiting room.

He hadn’t learned a hell of a lot, he thought. He’d known that Duckworth had gone to Mendez, and he already had the Hotel Byron address. There was, however, some negative information there. The last address they had was on Mendez, and yet Scholar Duckworth couldn’t be found on Mendez. Obviously, he had not filed a change of address there; just as obviously, he had managed to leave the planet without a trace. There was always the possibility that he’d been killed, of course. On a thinly populated world like Mendez, murder could still be committed with little chance of being caught. Even here on Earth, a murderer with the right combination of skill and luck could remain unsuspected.

But who would want to kill Scholar Duckworth?

And why?

Turnbull pushed the thought out of his mind. It was possible that Duckworth was dead, but it was highly unlikely. It was vastly more probable that the old scholar had skipped off for reasons of his own and that something had happened to prevent him from contacting Turnbull.

After all, almost the same thing had happened in reverse a year ago.

Outside the Terminal Building, Turnbull walked over to a hackstand and pressed the signal button on the top of the control column. An empty cab slid out of the traffic pattern and pulled up beside the barrier which separated the vehicular traffic from the pedestrian walkway. The gate in the barrier slid open at the same time the cab door did, and Turnbull stepped inside and sat down. He dialed his own number, dropped in the indicated number of coins, and then relaxed as the cab pulled out and sped down the freeway towards Manhattan.

He’d been back on Earth now for three days, and the problem of Scholar James Duckworth was still bothering him. He hadn’t known anything about it until he’d arrived at his apartment after a year’s absence.

The apartment door sighed a little as Dave Turnbull broke the electronic seal with the double key. Half the key had been in his possession for a year, jealousy guarded against loss during all the time he had been on Lobon; the other half had been kept by the manager of the Excelsior Apartments.

As the door opened, Turnbull noticed the faint musty odor that told of long-unused and poorly circulated air. The conditioners had been turned down to low power for a year now.

He went inside and allowed the door to close silently behind him. The apartment was just the same--the broad expanse of pale blue rug, the matching furniture, including the long, comfortable couch and the fat overstuffed chair--all just as he’d left them.

He ran a finger experimentally over the top of the table near the door. There was a faint patina of dust covering the glossy surface, but it was very faint, indeed. He grinned to himself. In spite of the excitement of the explorations on Lobon, it was great to be home again.

He went into the small kitchen, slid open the wall panel that concealed the apartment’s power controls, and flipped the switch from “maintenance” to “normal.” The lights came on, and there was a faint sigh from the air conditioners as they began to move the air at a more normal rate through the rooms.

Then he walked over to the liquor cabinet, opened it, and surveyed the contents. There, in all their glory, sat the half dozen bottles of English sherry that he’d been dreaming about for twelve solid months. He took one out and broke the seal almost reverently.

Not that there had been nothing to drink for the men on Lobon: the University had not been so blue-nosed as all that. But the choice had been limited to bourbon and Scotch. Turnbull, who was not a whisky drinker by choice, had longed for the mellow smoothness of Bristol Cream Sherry instead of the smokiness of Scotch or the heavy-bodied strength of the bourbon.

He was just pouring his first glass when the announcer chimed. Frowning, Turnbull walked over to the viewscreen that was connected to the little eye in the door. It showed the face of--what was his name? Samson? Sanders. That was it, Sanders, the building superintendent.

Turnbull punched the opener and said: “Come in. I’ll be right with you, Mr. Sanders.”

Sanders was a round, pleasant-faced, soft-voiced man, a good ten years older than Turnbull himself. He was standing just inside the door as Turnbull entered the living room; there was a small brief case in his hand. He extended the other hand as Turnbull approached.

“Welcome home again, Dr. Turnbull,” he said warmly. “We’ve missed you here at the Excelsior.”

Turnbull took the hand and smiled as he shook it. “Glad to be back, Mr. Sanders; the place looks good after a year of roughing it.”

The superintendent lifted the brief case. “I brought up the mail that accumulated while you were gone. There’s not much, since we sent cards to each return address, notifying them that you were not available and that your mail was being held until your return.”

He opened the brief case and took out seven standard pneumatic mailing tubes and handed them to Turnbull.

Turnbull glanced at them. Three of them were from various friends of his scattered over Earth; one was from Standard Recording Company; the remaining three carried the return address of James M. Duckworth, Ph. Sch., U.C.L.A., Great Los Angeles, California.

“Thanks, Mr. Sanders,” said Turnbull. He was wondering why the man had brought them up so promptly after his own arrival. Surely, having waited a year, they would have waited until they were called for.

Sanders blinked apologetically. “Uh ... Dr. Turnbull, I wonder if ... if any of those contain money ... checks, cash, anything like that?”

“I don’t know. Why?” Turnbull asked in surprise.

Sanders looked even more apologetic. “Well, there was an attempted robbery here about six months ago. Someone broke into your mailbox downstairs. There was nothing in it, of course; we’ve been putting everything into the vault as it came in. But the police thought it might be someone who knew you were getting money by mail. None of the other boxes were opened, you see, and--” He let his voice trail off as Turnbull began opening the tubes.

None of them contained anything but correspondence. There was no sign of anything valuable.

“Maybe they picked my box at random,” Turnbull said. “They may have been frightened off after opening the one box.”

“That’s very likely it,” said Sanders. “The police said it seemed to be a rather amateurish job, although whoever did it certainly succeeded in neutralizing the alarms.”

Satisfied, the building superintendent exchanged a few more pleasantries with Turnbull and departed. Turnbull headed back toward the kitchen, picked up his glass of sherry, and sat down in the breakfast nook to read the letters.

The one from Standard Recording had come just a few days after he’d left, thanking him for notifying them that he wanted to suspend his membership for a year. The three letters from Cairo, London, and Luna City were simply chatty little social notes, nothing more.

The three from Scholar Duckworth were from a different breed of cat.

The first was postmarked 21 August 2187, three months after Turnbull had left for Lobon. It was neatly addressed to Dave F. Turnbull, Ph.D.

Dear Dave (it read):

I know I haven’t been as consistent in keeping up with my old pupils as I ought to have been. For this, I can only beat my breast violently and mutter mea culpa, mea culpa, mea maxima culpa. I can’t even plead that I was so immersed in my own work that I hadn’t the time to write, because I’m busier right now than I’ve been for years, and I’ve had to make time for this letter.

Of course, in another way, this is strictly a business letter, and it does pertain to my work, so the time isn’t as hard to find as it might be.

But don’t think I haven’t been watching your work. I’ve read every one of your articles in the various journals, and I have copies of all four of your books nestled securely in my library. Columbia should be--and apparently is--proud to have a man of your ability on its staff. At the rate you’ve been going, it won’t be long before you get an invitation from the Advanced Study Board to study for your Scholar’s degree.

As a matter of fact, I’d like to make you an offer right now to do some original research with me. I may not be a top-flight genius like Metternick or Dahl, but my reputation does carry some weight with the Board. (That, Turnbull thought, was a bit of needless modesty; Duckworth wasn’t the showman that Metternick was, or the prolific writer that Dahl was, but he had more intelligence and down-right wisdom than either.) So if you could manage to get a few months leave from Columbia, I’d be honored to have your assistance. (More modesty, thought Turnbull. The honor would be just the other way round.)

The problem, in case you’re wondering, has to do with the Centaurus Mystery; I think I’ve uncovered a new approach that will literally kick the supports right out from under every theory that’s been evolved for the existence of that city. Sound interesting?

I’m mailing this early, so it should reach you in the late afternoon mail. If you’ll be at home between 1900 and 2000, I’ll call you and give you the details. If you’ve got a pressing appointment, leave details with the operator.

All the best,

Jim Duckworth

Turnbull slid the letter back into its tube and picked up the second letter, dated 22 August 2187, one day later.

Dear Dave,

I called last night, and the operator said your phone has been temporarily disconnected. I presume these letters will be forwarded, so please let me know where you are. I’m usually at home between 1800 and 2300, so call me collect within the next three or four days.

All the best,

Jim

The third letter was dated 10 November 2187. Turnbull wondered why it had been sent. Obviously, the manager of the Excelsior had sent Duckworth a notice that Dr. Turnbull was off-planet and could not be reached. He must have received the notice on the afternoon of 22 August. That would account for his having sent a second letter before he got the notice. Then why the third letter?

Dear Dave,

I know you won’t be reading this letter for six months or so, but at least it will tell you where I am. I guess I wasn’t keeping as close tabs on your work as I thought: otherwise I would have known about the expedition to Lobon. You ought to be able to make enough credit on that trip to bring you to the attention of the Board.

And don’t feel too bad about missing my first letters or the call. I was off on a wild goose chase that just didn’t pan out, so you really didn’t miss a devil of a lot.

As a matter of fact, it was rather disappointing to me, so I’ve decided to take a long-needed sabbatical leave and combine it with a little research on the half-intelligent natives of Mendez. I’ll see you in a year or so.

As ever,

Jim Duckworth

Well, that was that, Turnbull thought. It galled him a little to think that he’d been offered a chance to do research with Scholar Duckworth and hadn’t been able to take it. But if the research hadn’t panned out ... He frowned and turned back to the first letter.

A theory that would “literally kick the supports right out from under every theory that’s been evolved for the existence of that city,” he’d said. Odd. It was unlike Duckworth to be so positive about anything until he could support his own theory without much fear of having it pulled to pieces.

Turnbull poured himself a second glass of sherry, took a sip, and rolled it carefully over his tongue.

The Centaurus Mystery. That’s what the explorers had called it back in 2041, nearly a century and a half before, when they’d found the great city on one of the planets of the Alpha Centaurus system. Man’s first interstellar trip had taken nearly five years at sublight velocities, and bing!--right off the bat, they’d found something that made interstellar travel worthwhile, even though they’d found no planet in the Alpha Centaurus system that was really habitable for man.

They’d seen it from space--a huge domed city gleaming like a great gem from the center of the huge desert that covered most of the planet. The planet itself was Marslike--flat and arid over most of its surface, with a thin atmosphere high in CO_2 and very short on oxygen. The city showed up very well through the cloudless air.

From the very beginning, it had been obvious that whoever or whatever had built that city had not evolved on the planet where it had been built. Nothing more complex than the lichens had ever evolved there, as thousands of drillings into the crust of the planet had shown.

Certainly nothing of near-humanoid construction could ever have come into being on that planet without leaving some trace of themselves or their genetic forebears except for that single huge city.

How long the city had been there was anyone’s guess. A thousand years? A million? There was no way of telling. It had been sealed tightly, so none of the sand that blew across the planet’s surface could get in. It had been set on a high plateau of rock, far enough above the desert level to keep it from being buried, and the transparent dome was made of an aluminum oxide glass that was hard enough to resist the slight erosion of its surface that might have been caused by the gentle, thin winds dashing microscopic particles of sand against its smooth surface.

Inside, the dry air had preserved nearly every artifact, leaving them as they had been when the city was deserted by its inhabitants at an unknown time in the past.

That’s right--deserted. There were no signs of any remains of living things. They’d all simply packed up and left, leaving everything behind.

Dating by the radiocarbon method was useless. Some of the carbon compounds in the various artifacts showed a faint trace of radiocarbon, others showed none. But since the method depends on a knowledge of the amount of nitrogen in the atmosphere of the planet of origin, the rate of bombardment of that atmosphere by high-velocity particles, and several other factors, the information on the radioactivity of the specimens meant nothing. There was also the likelihood that the carbon in the various polymer resins came from oil or coal, and fossil carbon is useless for radio-dating.

Nor did any of the more modern methods show any greater success.

It had taken Man centuries of careful comparison and cross-checking to read the evolutionary history written in the depths of his own planet’s crust--to try to date the city was impossible. It was like trying to guess the time by looking at a faceless clock with no hands.

There the city stood--a hundred miles across, ten thousand square miles of complex enigma.

It had given Man his first step into the ever-widening field of Cultural Xenology.

Dave Turnbull finished his sherry, got up from the breakfast nook, and walked into the living room, where his reference books were shelved. The copy of Kleistmeistenoppolous’ “City of Centaurus” hadn’t been opened in years, but he took it down and flipped it open to within three pages of the section he was looking for.

“It is obvious, therefore, that every one of the indicators points in the same direction. The City was not--could not have been--self-supporting. There is no source of organic material on the planet great enough to support such a city; therefore, foodstuffs must have been imported. On the other hand, it is necessary to postulate some reason for establishing a city on an otherwise barren planet and populating it with an estimated six hundred thousand individuals.

“There can be only one answer: The race that built the City did so for the same reason that human beings built such megalopolises as New York, Los Angeles, Tokyo, and London--because it was a focal point for important trade routes. Only such trade routes could support such a city; only such trade routes give reason for the City’s very existence.

“And when those trade routes changed or were supplanted by others in the course of time, the reason for the City’s existence vanished.”

Turnbull closed the book and shoved it back into place. Certainly the theory made sense, and had for a century. Had Duckworth come across information that would seem to smash that theory?

The planet itself seemed to be perfectly constructed for a gigantic landing field for interstellar ships. It was almost flat, and if the transhipping between the interstellar vessels had been done by air, there would be no need to build a hard surface for the field. And there were other indications. Every fact that had come to light in the ensuing century had been in support of the Greek-German xenologist’s theory.

Had Duckworth come up with something new?

If so, why had he decided to discard it and forget his new theory?

If not, why had he formulated the new theory, and on what grounds?

Turnbull lit a cigarette and looked sourly at the smoke that drifted up from its tip. What the devil was eating him? He’d spent too much time away from Earth, that was the trouble. He’d been too deeply immersed in his study of Lobon for the past year. Now all he had to do was get a little hint of something connected with cultural xenology, and his mind went off on dizzy tizzies.

Forget it. Duckworth had thought he was on to something, found out that he wasn’t, and discarded the whole idea. And if someone like Scholar James Duckworth had decided it wasn’t worth fooling with, then why was a common Ph. D. like Turnbull worrying about it? Especially when he had no idea what had started Duckworth off in the first place.

And his thoughts came back around to that again. If Duckworth had thought enough of the idea to get excited over it, what had set him off? Even if it had later proved to be a bad lead, Turnbull felt he’d like to know what had made Duckworth think--even for a short time--that there was some other explanation for the City.

Ah, hell! He’d ask Duckworth some day. There was plenty of time.

He went over to the phone, dialed a number, and sat down comfortably in his fat blue overstuffed chair. It buzzed for half a minute, then the telltale lit up, but the screen remained dark.

“Dave!” said a feminine voice. “Are you back? Where on Earth have you been?”

“I haven’t,” said Turnbull. “How come no vision?”

“I was in the hammam, silly. And what do you mean ‘I haven’t’? You haven’t what?”

“You asked me where on Earth I’d been, and I said I haven’t.”

“Oh! Lucky man! Gallivanting around the starways while us poor humans have to stay home.”

“Yeah, great fun. Now look, Dee, get some clothes on and turn on your pickup. I don’t like talking to gray screens.”

“Half a sec.” There was a minute’s pause, then the screen came on, showing the girl’s face. “Now, what do you have on your purported mind?”

“Simple. I’ve been off Earth for a year, staring at bearded faces and listening to baritone voices. If it isn’t too short notice, I’d like to take you to dinner and a show and whatever else suggests itself afterward.”

“Done!” she said. “What time?”

“Twenty hundred? At your place?”

“I’ll be waiting.”

Dave Turnbull cut the circuit, grinning. The Duckworth problem had almost faded from his mind. But it flared back up again when he glanced at the mail tubes on his desk.

“Damn!” he said.

He turned back to the phone, jammed a finger into the dial and spun it angrily. After a moment, the screen came to life with the features of a beautifully smiling but obviously efficient blond girl.

“Interstellar Communications. May I serve you, sir?”

“How long will it take to get a message to Mendez? And what will it cost?”

“One moment, sir.” Her right hand moved off-screen, and her eyes shifted to look at a screen that Turnbull couldn’t see. “Mendez,” she said shortly. “The message will reach there in five hours and thirty-six minutes total transmission time. Allow an hour’s delay for getting the message on the tapes for beaming.

“The cost is one seventy-five per symbol. Spaces and punctuation marks are considered symbols. A, an, and, and the are symbols.”

Turnbull thought a moment. It was high--damned high. But then a man with a bona fide Ph. D. was not exactly a poor man if he worked at his specialty or taught.

“I’ll call you back as soon as I’ve composed the message,” he said.

“Very well, sir.”

He cut the circuit, grabbed a pencil and started scribbling. When he’d finished reducing the thing to its bare minimum, he started to dial the number again. Then he scowled and dialed another number.

This time, a mild-faced young man in his middle twenties appeared. “University of California in Los Angeles. Personnel Office. May I serve you?”

“This is Dr. Dave Turnbull, in New York. I understand that Scholar Duckworth is on leave. I’d like his present address.”

The young man looked politely firm. “I’m sorry, doctor; we can not give out that information.”

“Oh, yap! Look here; I know where he is; just give me--” He stopped. “Never mind. Let me talk to Thornwald.”

Thornwald was easier to deal with, since he knew both Duckworth and Turnbull. Turnbull showed him Duckworth’s letter on the screen. “I know he’s on Mendez; I just don’t want to have to look all over the planet for him.”

“I know, Dave. I’m sure it’s all right. The address is Landing City, Hotel Byron, Mendez.”

“Thanks, Thorn; I’ll do you a favor some day.”

“Sure. See you.”

Turnbull cut off, dialed Interstellar Communications, sent his message, and relaxed. He was ready to make a night of it. He was going to make his first night back on Earth a night to remember.

He did.

The next morning, he was feeling almost flighty. He buzzed and flitted around his apartment as though he’d hit a high point on a manic cycle, happily burbling utter nonsense in the form of a perfectly ridiculous popular song.

_My dear, the merest touch of you

Has opened up my eyes;

And if I get too much of you,

You really paralyze!

Donna, Donna, bella Donna,

Clad in crimson bright,

Though I’m near you, I don’t wanna

See the falling shades of night!_

Even when the phone chimed in its urgent message, it didn’t disturb his frothy mood. But three minutes later he had dropped down to earth with a heavy clunk.

His message to Mendez had not been delivered. There was not now, and never had been a Scholar James Duckworth registered at the Hotel Byron in Landing City. Neither was his name on the incoming passenger lists at the spaceport at Landing City.

He forced himself to forget about it; he had a date with Dee again that night, and he was not going to let something silly like this bother him. But bother him it did. Unlike the night before, the date was an utter fiasco, a complete flop. Dee sensed his mood, misinterpreted it, complained of a headache, and went home early. Turnbull slept badly that night.

Next morning, he had an appointment with one of the executives of U.C.L.I.--University of Columbia in Long Island--and, on the way back he stopped at the spaceport to see what he could find out. But all he got was purely negative information.

On his way back to Manhattan, he sat in the autocab and fumed.

When he reached home, he stalked around the apartment for an hour, smoking half a dozen cigarettes, chain fashion, and polishing off three glasses of Bristol Cream without even tasting it.

Dave Turnbull, like any really top-flight investigator, had developed intuitive thinking to a fine art. Ever since the Lancaster Method had shown the natural laws applying to intuitive reasoning, no scientist worthy of the name failed to apply it consistently in making his investigations. Only when exact measurement became both possible and necessary was there any need to apply logic to a given problem.

A logician adds two and two and gets four; an intuitionist multiplies them and gets the same answer. But a logician, faced with three twos, gets six--an intuitionist gets eight. Intuition will get higher orders of answers from a given set of facts than logic will.

Turnbull applied intuition to the facts he knew and came up with an answer. Then he phoned the New York Public Library, had his phone connected with the stacks, and spent an hour checking for data that would either prove or disprove his theory. He found plenty of the former and none of the latter.

Then he called his superiors at Columbia.

He had to write up his report on the Lobon explorations. Would it be possible for him to take a six-month leave of absence for the purpose?

It would.

The following Saturday, Dr. Dave F. Turnbull was on the interstellar liner Oriona, bound for Sirius.

If ever there was a Gold Mine In The Sky, it was Centaurus City. To the cultural xenologists who worked on its mysterious riches, it seemed to present an almost inexhaustible supply of new data. The former inhabitants had left everything behind, as though it were no longer of any value whatever. No other trace of them had as yet been found anywhere in the known galaxy, but they had left enough material in Centaurus City to satisfy the curiosity of Mankind for years to come, and enough mystery and complexity to whet that curiosity to an even sharper degree.

It’s difficult for the average person to grasp just how much information can be packed into a city covering ten thousand square miles with a population density equal to that of Manhattan. How long would it take the hypothetical Man From Mars to investigate New York or London if he had only the City to work with, if he found them just as they stand except that the inhabitants had vanished?

The technological level of the aliens could not be said to be either “above” or “below” that of Man: it could only be said to be “different.” It was as if the two cultures complemented each other; the areas of knowledge which the aliens had explored seemed to be those which Mankind had not yet touched, while, at the same time, there appeared to be many levels of common human knowledge which the aliens had never approached.

From the combination of the two, whole new fields of human thought and endeavor had been opened.

No trace of the alien spaceships had been uncovered, but the anti-gravitational devices in their aircraft, plus the basic principles of Man’s own near-light-velocity drive had given Man the ultralight drive.

Their knowledge of social organization and function far exceeded that of Man, and the hints taken from the deciphered writings of the aliens had radically changed Man’s notions of government. Now humanity could build a Galactic Civilization--a unity that was neither a pure democracy nor an absolute dictatorship, but resulted in optimum governmental control combined with optimum individual freedom. It was e pluribus unum plus. Their technological writings were few, insofar as physics and chemistry were concerned. What there were turned out to be elementary texts rather than advanced studies--which was fortunate, because it had been through these that the cultural xenologists had been able to decipher the language of the aliens, a language that was no more alien to the modern mind than, say, ancient Egyptian or Cretan.