'You sneezed, and met a girl, and not another. As a consequence, you made certain decisions, and so did the girl, and so did the girl you didn't meet, and the man who did meet her, and the people you all met thereafter. And your family, her family, their family - and your children.

'Because you sneezed twenty years ago, five people, or fifty, or five hundred, might be dead now who would have been alive, or might be alive who would have been dead. Move it to two hundred years ago: two thousand years ago, and a sneeze - even by someone no history ever heard of - might have meant that no one now alive would have been alive.'

The Boss rubbed the back of his head: 'Widening ripples. I read a story once -'

'So did I. It's not a new idea - but I want you to think about it for a while, because I want to read to you from an article by Professor Elmer Tywood in a magazine twenty years old. It was just before the last war.'

I had copies of the film in my pocket and the white wall made a beautiful screen, which was what it was meant to do. The boss made a motion to turn about, but I waved him back.

'No, sir,' I said. 'I want to read this to you. And I want you to listen to it.'

He leaned back.

'The article,' I went on, is entitled: "Man's First Great Failure!" Remember, this was just before the war, when the bitter disappointment at the final failure of the United Nations was at its height. What I will read are some excerpts from the first part of the article. It goes like this:

'"… That Man, with his technical perfection, has failed to solve the great sociological problems of today is only the second immense tragedy that has come to the race. The first, and perhaps the greater, was that, once, these same great sociological problems -were solved; and yet these solutions were not permanent, because the technical perfection we have today did not then exist.

'"It was a case of having bread without butter, or butter without bread. Never both together…

' "Consider the Hellenic world, from which our philosophy, our mathematics, our ethics, our art, our literature - our entire culture, in fact - stem… In the days of Pericles, Greece, like our own world in microcosm, was a surprisingly modern pot pourri of conflicting ideologies and ways of life. But then Rome came, adopting the culture, but bestowing, and enforc ing, peace. To be sure, the Pax Romano lasted only two hun dred years, but no like period has existed since…

' "War was abolished. Nationalism did not exist. The Roman citizen was Empire-wide. Paul of Tarsus and Flavius Josephus were Roman citizens. Spaniards, North Africans, Illyrians assumed the purple. Slavery existed, but it was an indiscriminate slavery, imposed as a punishment, incurred as the price of economic failure, brought on by the fortunes of war. No man was a natural slave - because of the color of his skin or the place of his birth.

'"Religious toleration was complete. If an exception was made early in the case of the Christians, it was because they refused to accept the principle of toleration; because they in sisted that only they themselves knew truth - a principle ab horrent to the civilized Roman…

' "With all of Western culture under a single polis, with the cancer of religious and national particularism and exclusiv-ism absent; with a high civilization in existence - why could not Man hold his gains?

' "It was because, technologically, ancient Hellenism remained backward. It was because without a machine civilization, the price of leisure - and hence civilization and culture -for the few, was slavery for the many. Because the civilization could not find the means to bring comfort and ease to all the population.

' "Therefore, the depressed classes turned to the other world, and to religions which spurned the material benefits of this world - so that science was made impossible in any true sense for over a millennium. And further, as the initial impetus of Hellenism waned, the Empire lacked the technological powers to beat back the barbarians. In fact, it was not till after a.d. 1500 that war became sufficiently a function of the industrial resources of a nation to enable the settled people to defeat invading tribesmen and nomads with ease…

'"Imagine, then, if somehow the ancient Greeks had learned just a hint of modern chemistry and physics. Imagine if the growth of the Empire had been accompanied by the growth of science, technology and industry. Imagine an Empire in which machinery replaced slaves, in which all men had a decent share of the world's goods, in which the legion became the armored column against which no barbarians could stand. Imagine an Empire which would therefore spread all over the world, without religious or national prejudices.

'"An Empire of all men - all brothers - eventually all free…

' "If history could be changed. If that first great failure could have been prevented -"'

And I stopped at that point.

'Well?'said the Boss.

'Well,' I said, 'I think it isn't difficult to connect all that with the fact that Tywood blew an entire power plant in his anxiety to send something back to the past, while in his office safe we found sections of a chemistry textbook translated into Greek.'

His face changed, while he considered.

Then he said heavily: 'But nothing's happened.'

'I know. But then I've been told by Tywood's student that it takes a day to move back a century in time. Assuming that ancient Greece was the target area, we have twenty centuries, hence twenty days.'

'But can it be stopped?'

'I wouldn't know. Tywood might, but he's dead.'

The enormity of it all hit me at once, deeper than it had the night before -

All humanity was virtually under sentence of death. And while that was merely horrible abstraction, the fact that reduced it to a thoroughly unbearable reality was that I was, too. And my wife, and my kid.

Further, it was a death without precedence. A ceasing to exist, and no more. The passing of a breath. The vanishing of a dream. The drift into eternal non-space and non-time of a shadow. I would not be dead at all, in fact. I would merely never have been born.

Or would I? Would I exist - my individuality - my ego - my soul, if you like? Another life? Other circumstances?

I thought none of that in words then. But if a cold knot in the stomach could ever speak under the circumstances, it would sound like that, I think.

The Boss moved in on my thoughts - hard.

'Then, we have about two and a half weeks. No time to lose. Come on.'

I grinned with one side of my mouth: 'What do we do? Chase the book?'

'No,' he replied coldly, 'but there are two courses of action we must follow. First, you may be wrong - altogether. All of this circumstantial reasoning may still represent a false lead, perhaps deliberately thrown before us, to cover up the real truth. That must be checked.

'Secondly, you may be right - but there may be some way of stopping the book: other than chasing it in a time machine, I mean. If so, we must find out how.'

'I would just like to say, sir, if this is a false lead, only a madman would consider it a believable one. So suppose I'm right, and suppose there's no way of stopping it?'

'Then, young fellow, I'm going to keep pretty busy for two and a half weeks, and I'd advise you to do the same. The time will pass more quickly that way.'

Of course he was right.

'Where do we start?' I asked.

'The first thing we need is a list of all men and women on the government payroll under Tywood.'

'Why?'

'Reasoning. Your specialty, you know. Tywood doesn't know Greek, I think we can assume with fair safety, so someone else must have done the translating. It isn't likely that anyone would do a job like that for nothing, and it isn't likely that Tywood would pay out of his personal funds - not on a professor's salary.'

'He might,' I pointed out, 'have been interested in more secrecy than a government payroll affords.'

'Why? Where was the danger? Is it a crime to translate a chemistry textbook into Greek? Who would ever deduce from that a plot such as you've described?'

It took us half an hour to turn up the name of Mycroft James Boulder, listed as 'Consultant,' and to find out that he was mentioned in the University Catalogue as Assistant Professor of Philosophy and to check by telephone that among his many accomplishments was a thorough knowledge of Attic Greek.

Which was a coincidence - because with the Boss reaching for his hat, the interoffice teletype clicked away and it turned out that Mycroft James Boulder was in the anteroom, at the end of a two-hour continuing insistence that he see the Boss.

The Boss put his hat back and opened his office door.

Professor Mycroft James Boulder was a gray man. His hair was gray and his eyes were gray. His suit was gray, too.

But most of all, his expression was gray; gray with a tension that seemed to twist at the lines in his thin face.

Boulder said, softly: 'I've been trying for three days to get a hearing, sir, with a responsible man. I can get no higher than yourself.'

'I may be high enough,' said the Boss. 'What's on your mind?'

'It is quite important that I be granted an interview with Professor Tywood.'

'Do you know where he is?'

'I am quite certain that he is in government custody.'

'Why?'

'Because I know that he was planning an experiment which would entail the breaking of security regulations. Events since, as nearly as I can make them out, flow naturally from the supposition that security regulations have indeed been broken. I can presume, then, that the experiment has at least been attempted. I must discover whether it has been successfully concluded.'

'Professor Boulder,' said the Boss, 'I believe you can read Greek.'

'Yes, I can,' - coolly.

'And have translated chemical texts for Professor Tywood on government money.'

'Yes - as a legally employed consultant'

'Yet such translation, under the circumstances, constitutes a crime, since it makes you an accessory to Tywood's crime.'

'You can establish a connection?'

'Can't you? Or haven't you heard of Tywood's notion on time travel, or… what do you call it… micro-temporal-trahslation?'

'Ah?' and Boulder smiled a little. 'He's told you, then.'

'No, he hasn't,' said the Boss, harshly. 'Professor Tywood is dead.'

'What?' Then - 'I don't believe you.'

'He died of apoplexy. Look at this.'

He had one of the photographs taken that first night in his wall safe. Tywood's face was distorted but recognizable -sprawled and dead.

Boulder 's breath went in and out as if the gears were clogged. He stared at the picture for three full minutes by the electric clock on the wall. 'Where is this place?' he asked.