On his first day as a mail carrier, Sam Wilson noted that inscription, cribbed from Herodotus, on the General Post Office, and took it to heart: "Not snow, nor rain, nor heat, nor gloom of night stays these couriers from the swift completion of their appointed rounds."

It couldn't be literally true, of course. Given a real blizzard, it would be impossible to make his way through the pathless drifts; and if there had been a major flood, he could hardly have swum to deliver letters to the marooned. Moreover, if he couldn't find the addressee, there was nothing to do but mark the envelope "Not known at this address," and take it back to be returned to the addresser or consigned to the Dead Letter Office. But through the years, Sam Wilson had been as consciously faithful and efficient as any Persian messenger.

Now the long years had galloped by, and this was the very last time he would walk his route before his retirement.

It would be good to put his feet up somewhere and ease them back into comfort; they had been Sam's loyal servants and they were more worn out than he was. But the thought of retirement bothered him. Mollie was going to get sick of having him around the house all day, and he was damned if he was going to sit on a park bench like other discarded old men and suck a pipe and stare at nothing, waiting for the hours to pass in a vacuum. He had his big interest, of course—his status as a devoted science fiction fan; he would have time now to read and reread, to watch hopefully from the roof of his apartment house for signs of a flying saucer. But that wasn't enough; what he needed was a project to keep him alert and occupied.

On his last delivery he found it.

The Ochterlonie Building, way down on lower Second Avenue, was a rundown, shabby old firetrap, once as solid as the Scotsman who had built it and named it for himself, but now, with its single open-cage elevator and its sagging floors, attracting only quack doctors and dubious private eyes and similar fauna on the edge of free enterprise. Sam had been delivering to it now for 35 years, watching its slow deterioration.

This time there was a whole batch of self-addressed letters for a tenant whose name was new to him, but that was hardly surprising—nowadays, in the Ochterlonie Building, tenants came and went.

They were small envelopes, addressed in blue, in printing simulating handwriting, to Orville K. Hesterson, Sec.-Treas., Time-Between-Time, 746 Ochterlonie Building, New York 3, N. Y. Feeling them with experienced fingers, Sam Wilson judged they were orders for something, doubtless enclosing money.

In most of the buildings on his last route, Sam knew, at least by sight, the employees who took in the mail, and they knew him. A lot of them knew this was his last trip; there were farewells and good wishes, and even a few small donations (since he wouldn't be there next Christmas) which he gratefully tucked in an inside pocket of the uniform he would never wear again. There were also two or three invitations to a drink, which, being still on duty, he had regretfully to decline.

But in the Ochterlonie Building, with its fly-by-night clientele, he was just the postman, and nobody greeted him except Howie Mallory, the decrepit elevator operator. Sam considered him soberly. It was going to be pretty tough financially from now on; could he, perhaps, find a job like Howie's? No. Not unless things got a lot tougher; standing all day would be just as bad as walking.

He went from office to office, getting rid of his load—mostly bills, duns and complaints, he imagined, in this hole. There was nothing for the seventh floor except this bunch for Time-Between-Time.

The seventh floor? He must be nuts. The Ochterlonie Building was six floors high.

Puzzled, he rang for Howie.

"What'd they do, build a penthouse office on top of this old dump?" he inquired.

The elevator operator laughed as at a feeble jest. "Sure," he said airily. "General Motors is using it as a hideaway."

"No, Howie—no fooling. Look here."

Mallory stared and shook his head. "There ain't no 746. Somebody got the number wrong. Or they got the building wrong. There's nobody here by that name."

"They couldn't—printed envelopes like these."

"O. K., wise guy," said Howie. "Look for yourself."

He led the way to the short flight of iron stairs and the trap door. While Mallory stood jeering at him, Sam determinedly climbed through. There was nothing in sight but the plain flat roof. He climbed down again.

"Last letters on my last delivery and I can't deliver them," Sam Wilson said disgustedly.

"Somebody's playing a joke, maybe."

"Crazy joke. Well, so long, Howie. Some young squirt will be taking his life in his hands in this broken-down cage of yours tomorrow."

Sam Wilson, whom nothing could deter from the swift completion of his appointed rounds, had to trudge back to the post office with 22 undelivered letters.

Years ago the United States Post Office gave up searching directories and reference books, or deciphering illiterate or screwy addresses, so as to make every possible delivery. That went out with three daily and two Saturday deliveries, two-cent drop postage, and all the other amenities that a submissive public let itself lose without a protest. But there was still a city directory in the office. Sam Wilson searched it stubbornly. Time-Between-Time was not listed. Neither was Orville K. Hesterson.

There was nothing to do but consider the letters nixies and turn them over to the proper department. If there was another bunch of them tomorrow, he would never know.

Retirement, after the first carefree week, was just as bad as Sam Wilson had suspected it was going to be. Not bad enough to think yet about elevator operating or night watching, but bad enough to make him restless and edgy, and to make him snap Mollie's head off until they had their first bad quarrel for years. He'd never had time enough before to keep up with all the science fiction magazines and books. Now, with nothing but time, there weren't enough of them to fill the long days. What he needed was something—something that didn't involve walking—to make those endless hours speed up. He began thinking again about those 22 nixies.

He sat gloomily on a bench in Tompkins Square in the spring sunshine: just what he had sworn not to do, but if he stayed home another hour, Mollie would heave the vacuum cleaner at him. In the public library he had searched directories and phone books, for all the boroughs and for suburban New Jersey, Connecticut and Pennsylvania; Orville K. Hesterson appeared in none of them.

He didn't know why it was any of his business, except that Time-Between-Time had put a blot on the very end of his 35-year record and he wanted revenge. Also, it was something to do and be interested in. In a way, science fiction and detection had a lot in common, and Sam Wilson prided himself on his ability to guess ahead what was going to happen in a story. So why couldn't he figure out this puzzle, right here in Manhattan, Terra? But he was stymied.

Or was he?

Sam took his gloomy thoughts to Mulligan's. Every large city is a collection of villages. The people who live long enough in a neighborhood acquire their own groceries, their own drugstores, their own bars. The Wilsons had lived six years in their flat, and Mulligan's, catercornered across the street, was Sam's personal bar.

He was cautious as to what he said there. He'd heard enough backtalk already when he had been indiscreet enough once, after four beers, to express his views on UFOs. He had no desire to gain a reputation as a crackpot. But it was safe enough to remark conversationally, "How do you find out where a guy is when he says he's someplace and you write him there and the letter comes back?"

"You ought to know, Sam," said Ed, the day barkeep. "You were a postman long enough."

"If I knew, I wouldn't ask."

"Ask Information on the phone."

"He hasn't got a phone." That was the weirdest part of it—a business office without a phone.

In every bar, at every moment, there is somebody who knows all the answers. This somebody, a nondescript fellow nursing a Collins down the bar, spoke up: "It could be unlisted."

Sam's acquaintance didn't include people with unlisted phones; he hadn't thought of that.

"Then how do you find out his number?"

"You don't, unless he tells you. That's why he has it unlisted."

The police could get it, Sam thought. But they wouldn't, without a reason.

"Hey, maybe this guy's office is in one of them flying saucers and he forgot to come down and get his mail," Ed suggested brightly.

Sam scowled and walked out.

Nevertheless....

Nothing to do with UFOs, of course. That was ridiculous.

But suppose there was a warp in the space-time continuum? Suppose there had once been another Ochterlonie Building, or some day in the future there was going to be another one, somewhere in New York? There wasn't another now, in any of the boroughs, or any other building with a name remotely like it; his research had already established that.

Sam went back to the Public Library. The building he knew had been erected in 1898. He consulted directories as far back as they went; there never had been one of the name before. Then a time-slip from the future?

That was hopeless, so far as he could do anything about it, so he cast about for another solution. How about a parallel world?

That could be, certainly: some accident by which mail for that other Ochterlonie Building, the seven-story one, had (maybe just once) arrived in the wrong dimension.

He couldn't do anything to prove or disprove that, either. What he needed was a break.

He got it.

One morning in early summer his own mailbox in the downstairs hallway disgorged a long envelope, addressed to Mr. Samuel Wilson. The upper left-hand corner bore a printed return address: Time-Between-Time, 746 Ochterlonie Building, New York 3, N. Y. He raced upstairs, locked himself in the bathroom, the one place Mollie couldn't interrupt him, and tore the envelope open with trembling fingers.

It was a form letter, with the "Dear Mr. Wilson" not too accurately typed in. It enclosed one of those blue-printed envelopes in simulated handwriting. The letterhead carried the familiar impossible address, but no phone number.

Maybe it was chance, maybe it was ESP, but he himself had got onto Time-Between-Time's mailing list!

He had trouble focusing his eyes to read the letter.

Sam Wilson read the letter three times. "It's crazy," he muttered. "It's a gyp."

What he ought to do was take the letter to the post office—Mr. Gross would be the one to see—and let them decide whether this Hesterson was using the mails to defraud. Let Mr. Gross and his department try to find 746 in the six-story Ochterlonie Building. As a faithful employee for 35 years, it was Sam's plain duty.

But then it would be out of his hands forever; he'd never even find out what happened. And he'd be back in the dull morass that retirement was turning out to be.

"Sam!" Mollie yelled outside the locked door. "Aren't you ever coming out of there?"

"I'm coming, I'm coming!" He put the letter and its enclosure back in the envelope and placed them in a pocket.

Time enough to decide that afternoon what he was going to do.

He escaped after lunch to what was becoming his refuge on a park bench. There he read the letter for the fourth time. For a long while he sat ruminating. About three o'clock he walked to the General Post Office—walking had become a habit hard to break—and hunted up the man who now had his old route, a youngster not more than 30 named Flanagan.

From the letter Sam extracted the return envelope.

"You been delivering any like this?" he asked.

Flanagan peered at it.

"Yeah," he said. "Plenty." He looked worried. "Gee, Wilson, I'm glad you came in. There's something funny about those deliveries, and I don't want to get in Dutch."

"Funny how?"

"My very first day on the route, I started up to the seventh floor of that building to deliver them—and there wasn't any seventh floor. So I asked the old elevator man—"

"Howie Mallory. I know him. He's been there for years."

"I guess so. Anyway, he said it was O. K. just to give them to him. He showed me a paper, signed with the name of this outfit, by the secretary or something—"

"Orville K. Hesterson," Sam said.

"That was it—saying that all mail for them was to be delivered to the elevator operator until further notice. So I've been giving it to him ever since—there's a big bunch every day. Is something wrong, Sam? Have I pulled a boner? Am I going to be in trouble?"

"No trouble. I'm just checking—little job they asked me to do for them, seeing I'm retired." Sam was surprised at the glibness with which that fib came out.

Flanagan looked still more worried. "He said their office was being remodeled or something, so he was looking after their mail till they could move in."

"Sure. Don't give it another thought." Another idea occurred to him; he lowered his voice. "I oughtn't to tell you this, Flanagan, but every new man on a route, they kind of check up on him the first few weeks, see if he's handling everything O.K. I'll tell them you're doing fine."

"Hey, thanks. Thanks a lot."

"Don't say anything about this. It's supposed to be secret."

"Oh, I won't."

Sam Wilson waved and walked out. He sat on the steps a while to think.

Was old Howie Mallory pulling a fast one? Was he Orville K. Hesterson? Had he cooked up a scheme to make himself some crooked money?

Three things against that. First, those nixies the first day: why wouldn't Mallory have told him the same thing he told Flanagan? Sam would have believed him, if he had said they were building an office on the roof and giving it a number.

Second, Howie just wasn't smart enough. Of course he could be fronting for the real crook. But Sam had known him for years, and old Howie had always seemed downright stupidly honest. A man doesn't suddenly turn into a criminal after a lifetime of probity.

Third, if this was some fraudulent scheme involving Mallory, nobody the old man knew—least of all the postman who used to deliver mail to that very building—would ever have been allowed to appear on the sucker list.

Sam Wilson thought some more. Then he hunted up the nearest pay phone and called Mollie.

"Mollie? Sam. Look, I just met an old friend of mine—" he picked a name from a billboard visible from the phone booth—"Bill Seagram, you remember him—oh, sure you do; you've just forgotten. Anyway, he's just here for the day and we're going to have dinner and see a show. Don't wait up for me. I might be pretty late.... No, I'm not phoning from Mulligan's.... Now you know me, Mollie; do I ever drink too much?... Yeah, sure, he ought to've asked you too, but he didn't. O.K., he's impolite. Aw, Mollie, don't be like that—"

She hung up on him.

Sam Wilson stood concealed in a doorway from which he could see the cramped lobby of the Ochterlonie Building. It was ten minutes before somebody entered it and rang for the elevator. The minute Howie Mallory started up with his passenger, Sam darted into the building and started climbing the stairs. He heard Mallory passing him, going down again, but the elevator wasn't visible from the stairway. On the sixth floor, after a quick survey to see that the hall was clear and the doors closed that he had to pass, he found the iron steps to the trapdoor.

The roof was just as empty as the other time he had visited it. No, it wasn't. In a corner by the parapet, weighted with a brick to keep it from blowing away, was a large paper bag. Sam picked up the brick and looked inside. It was stuffed with those blue-printed return envelopes.

He looked carefully about him. There were buildings all around, towering over the little old Ochterlonie Building. There were plenty of windows from which a curious eye could discern anything happening on that roof. But at night anybody in those buildings would be either working late or cleaning offices, with no reason whatever to go to a window; and Sam was sure nothing was going to happen till after dark.

It was a warm day and he had been carrying his coat. He folded it and put it down near the paper bag and sat on it with his back against the parapet. He cursed himself for not having had more foresight; he should have brought something to eat and something to read. Well, he wasn't going to climb down all those stairs and up again. He lighted his pipe and began waiting.

He must have dozed off, for he came to himself with a start and found it was almost dark. The paper bag was still there. It was just as well he had slept; now he'd have no trouble staying awake and watching. He might very well be there all night—in fact, he'd have to be, whether anything happened or not. The front door would be locked by now. Mollie would have a fit, but he had his alibi ready.

There was only one explanation left. Not time travel. Not alternate universes. Not an ordinary confidence game. Not—decidedly not—a hoax.

If he was wrong, then tomorrow morning he'd take the whole business to Mr. Gross. But he had a hunch he wasn't going to be wrong.

It was 12:15 by his wristwatch when he saw it coming.

It had no lights; nobody could have spotted it as it appeared suddenly out of nowhere and climbed straight down. It landed lightly as a drop of dew. The port opened and a small, spare man, very neatly dressed, as Sam could see with eyes accustomed to the darkness, stepped out. Orville K. Hesterson in person.

He tiptoed quickly to the paper bag. Then he saw Sam and stopped short. Sam reached out and grabbed a wrist. It felt like flesh, but he couldn't be sure.

"Who are you? What are you doing here?" the newcomer said in a strained whisper, just like a scared character in a soap opera. So he spoke English. Good: Sam didn't speak anything else.

"I'm from the United States Post Office," Sam replied suavely. Well, he had been, long enough, hadn't he?

"Oh. Well, now look, my friend—"

" You look. Talk. How much are you paying the elevator operator to put your mail up here every day?"

"Five dollars a day, in dollar bills, six days a week, left in the empty bag," answered Hesterson—it must be Hesterson—sullenly. "That's no crime, is it? Call this my office, and call that my rent. All I need an office for is to have somewhere to get my letters."

"Letters with money in them."

"We have to have funds for postage, don't we?"

"What about the postage on the first mailing list, before you got any dollars to pay for stamps?"

If it had been a little lighter, Sam would have been surer of the alarm that crossed Hesterson's face.

"I—well, we had to fabricate some of your currency for that. We regretted it—we aim to obey all local rules and regulations. As soon as we have enough coming in, we intend to send the amount to the New York postmaster as anonymous conscience money."

"How about the $1,000 prize? And those dollar book credits?"

"Oh, that. Well, we say ' when our publishing firm has been established,' don't we? That publishing thing is just a gimmick. As for the $1,000, we give no intimation of when the poll will end."

Sam tightened his grasp on the wrist, which was beginning to wriggle.

"I see. O.K., explain the whole setup. It sounds crazy to me."

"I couldn't agree with you more," said Mr. Hesterson, to Sam's surprise. "That's exactly what, in our own idiom, I told—" Sam couldn't get the name; it sounded like a grunt. "But he's the boss and I'm only a scout third class." His voice grew plaintive. "You can't imagine what an ordeal it is, almost every week, to have to land in a secluded place where I can hide the flyer, make my way to New York, and buy a bunch of stamps and mail a batch of letters in broad daylight. We can simulate your paper and printing and typing well enough, but"—that grunt again—"insists we use genuine stamps. I told you we try to follow all your laws, as far as we possibly can. It's very difficult for me to keep this absurd shape for long at a time; I'm exhausted after every trip. I can assure you, these little night excursions from the mother-ship to pick up the letters are the very least of my burdens!"

"What in time does your boss think he's going to gain by such a screwy come-on?"

"'In time'? Oh, just an idiomatic phrase. Like our calling our organization Time-Between-Time, time of course being just a dimension of space. I learned your tongue mostly from the B.B.C. and I don't always understand your speech in New York. My dear sir, do you here on this planet ask your bosses why they concoct their plans? Mine has a very profound mind; that's why he is the boss. All I know is that he persuaded the Council to try it out. A softening-up process—isn't that what you people call it when you use it in your silly wars with one another?"

"Softening for what?" But Sam Wilson knew the answer already.

"Why, for the invasion, of course," said Orville K. Hesterson, whose own name was probably a grunt. "Surely you must be aware that, with planetwide devastation likely and even imminent, every world whose inhabitants can live comfortably under extreme radiation is looking to yours—Earth, as you call it—as a possible area for colonization? So many planets are so terribly overcrowded—there's always a rush for a new frontier. We've missed out too often; this time we're determined to be first."

"I'll be darned," said Sam, "if I can see how that questionnaire would be any help to you."

"But it's elementary, as I believe one of your famous law-enforcers once declared. First of all, we're gaining a pretty good idea of what kind of reception we're likely to meet when we arrive, and therefore whether we're going to need weapons to destroy what will be left of the population, or can reasonably expect to take over without difficulty. We figure that a cross-section of one of your largest cities will be a pretty good indication, and we can extrapolate from that. In the second place, the question itself is deliberately worded to startle the recipients, who have never in their lives contemplated such a thing as an extraterrestrial visitor—"

"Not me. I'm a science fiction fan from way back. It's all old stuff to me."

Hesterson clicked his tongue—or at least the tongue he was wearing. "Oh, dear, that was an error. We tried particularly not to include on our lists subscribers to any of your speculative periodicals. That wasn't my mistake, thank goodness; it was another scout who had the horrible job of spending several days here and compiling the lists. Under your present low radioactivity it's real agony for us."

"I'll tell you one mistake you did make, though," said Sam angrily. "You ought to've arranged with the elevator man before your first lot of answers was due. If you want to know, that's how I got onto the whole thing. I'm a mail carrier—I'm retired now, but I was then—and I was the one supposed to deliver the first batch. Mallory—that's the elevator operator—laughed in my face and told me there wasn't any 746 in this building, and I had to take the letters back to the post office—on my last delivery!" Sam couldn't keep the bitterness out of his voice. "After 35 years—well, that's neither here nor there. But I didn't like that and I made up my mind to find out what was happening."

"So that's it. Oh, dear, dear. I'll have to compensate for that or I will be in trouble."

Sam had had enough. "You are in trouble right now," he growled, pushing the little alien back against the parapet. "We're staying right here till morning, and then I'm going to call for help and take you and your flying saucer or whatever it is straight to the F.B.I."

The counterfeit Mr. Hesterson laughed.

"Oh, no indeed you aren't," he said mildly. "I can slip right back into my own shape whenever I want to—the only reason I haven't done it yet is that then I wouldn't have the equipment to talk to you—and I assure you that you couldn't hold me then. On the contrary. As you just pointed out to me, I did make one bad error, and my boss doesn't like errors. I have no intention of making another one by leaving you here to spread the news."

"What do you mean?" Sam Wilson cried. For the first time, after the years of accustomedness to the idea of extraterrestrial beings, a thrill of pure terror shot through him.

"This," said the outsider softly.

Before Sam could take another breath, the wrist he was holding slid from his grasp, all of Mr. Hesterson slithered into something utterly beyond imagining, and Sam found himself enveloped in invisible chains against which he was unable to make the slightest struggle. He felt himself being lifted and thrown into the cockpit. Something landed on top of him—undoubtedly the package of prize entries and dollar bills. His last conscious thought was a despairing one of Mollie.

Sam Wilson, devoted mail carrier, was making a longer trip than any Persian courier ever dreamed of, and not snow, nor rain, nor heat, nor gloom of night could stay him from his appointed round.

But he may not be gone forever. If he can be kept alive on that planet in some other solar system, they plan to bring him back as Exhibit One whenever World War III has made Earth sufficiently radioactive for Orville K. Hesterson's co-planetarians to live here comfortably.