"Time travel has been written up in fiction; it has been discussed otherwise as an impossibility. Then we discover that the Reds have it working----"

"You mean, they go into the future and bring back machines to use now."

The major shook his head. "Not the future, the past."

Was this an elaborate joke? Somewhat heatedly Ross snapped out the answer to that. "Look here, I know I haven't the education of your big brains, but I do know that the farther back you go into history the simpler things are. We ride in cars; only a hundred years ago men drove horses. We have guns; go back a little and you'll find them waving swords and shooting guys with bows and arrows--those that don't wear tin plate on them to stop being punctured----"

"Only they were, after all," commented Ashe. "Look at Agincourt, m'lad, and remember what arrows did to the French knights in armor."

Ross disregarded the interruption. "Anyway"--he stuck doggedly to his point--"the farther back you go, the simpler things are. How are the Reds going to find anything in history we can't beat today?"

"That is a point which has baffled us for several years now," the major returned. "Only it is not _how_ they are going to find it, but _where_.

Because somewhere in the past of this world they have contacted a civilization able to produce weapons and ideas so advanced as to baffle our experts. We have to find that source and either mine it ourselves or close it off. As yet we're still trying to find it."

Ross shook his head. "It must be a long way back. Those guys who discover tombs and dig up old cities--couldn't they give you some hints?

Wouldn't a civilization like that have left something we could find today?"

"It depends," Ashe remarked, "upon the type of civilization. The Egyptians built in stone, grandly. They used tools and weapons of copper, bronze, and stone, and they were considerate enough to operate in a dry climate which preserved relics well. The cities of the Fertile Crescent built in mud brick and used stone, copper, and bronze tools.

They also chose a portion of the world where climate was a factor in keeping their memory green.

"The Greeks built in stone, wrote their books, kept their history to bequeath it to their successors, and so did the Romans. And on this side of the ocean the Incas, the Mayas, the unknown races before them, and the Aztecs of Mexico all built in stone and worked in metal. And stone and metal survive. But what if there had been an early people who used plastics and brittle alloys, who had no desire to build permanent buildings, whose tools and artifacts were meant to wear out quickly, perhaps for economic reasons? What would they leave us--considering, perhaps, that an ice age had intervened between their time and ours, with glaciers to grind into dust what little they did possess?

"There is evidence that the poles of our world have changed and that this northern region was once close to being tropical. Any catastrophe violent enough to bring about a switch in the poles of this planet might well have wiped out all traces of a civilization, no matter how superior. We have good reason to believe that such a people must have existed, but we must find them.

"And Ashe is a convert from the skeptics--" the major slipped down from his perch on the wall shelf--"he is an archaeologist, one of your tomb discoverers, and knows what he is talking about. We must do our hunting in time earlier than the first pyramid, earlier than the first group of farmers who settled by the Tigris River. But we have to let the enemy guide us to it. That's where you come in."

"Why me?"

"That is a question to which our psychologists are still trying to find the answer, my young friend. It seems that the majority of the people of the several nations linked together in this project have become too civilized. The reactions of most men to given sets of circ.u.mstances have become set in regular patterns and they cannot break that conditioning, or if personal danger forces them to change those patterns, they are afterward so adrift they cannot function at their highest potential.

Teach a man to kill, as in war, and then you have to recondition him later.

"But during these same wars we also develop another type. He is the born commando, the secret agent, the expendable man who lives on action.

There are not many of this kind, and they are potent weapons. In peacetime that particular collection of emotions, nerve, and skills becomes a menace to the very society he has fought to preserve during a war. He is pressured by the peaceful environment into becoming a criminal or a misfit.

"The men we send out from here to explore the past are not only given the best training we can possibly supply for them, but they are all of the type once heralded as the frontiersman. History is sentimental about that type--when he is safely dead--but the present finds him difficult to live with. Our time agents are misfits in the modern world because their inherited abilities are born out of season now. They must be young enough and possess a certain brand of intelligence to take the stiff training and to adapt, and they must pa.s.s our tests. Do you understand?"

Ross nodded. "You want crooks because they are crooks----"

"No, not because they are crooks, but because they are misfits in their time and place. Don't, I beg of you, Murdock, think that we are operating a penal inst.i.tution here. You would never have been recruited if you hadn't tested out to suit us. But the man who may be labeled murderer in his own period might rank as a hero in another, an extreme example, but true. When we train a man he not only can survive in the period to which he is sent, but he can also pa.s.s as a native born in that era----"

"What about Hardy?"

The major gazed into s.p.a.ce. "There is no operation which is foolproof.

We have never said that we don't run into trouble or that there is no danger in this. We have to deal with both natives of different times, and if we are lucky and hit a hot run, with the Reds. They suspect that we are casting about, hunting their trail. They managed to plant Kurt Vogel on us. He had an almost perfect cover and conditioning. Now you have it straight, Murdock. You satisfy our tests, and you'll be given a chance to say yes or no before your first run. If you say no and refuse duty, it means you must become an exile and stay here. No man who has gone through our training can return to normal life; there is too much chance of his being picked up and sweated by the opposition."

"Never?"

The major shrugged. "This may be a long-term operation. We hope not, but there is no way of telling now. You will be in exile until we either find what we want or fail entirely. That is the last card I have to lay on the table." He stretched. "You're slated for training tomorrow. Think it over and then let us know your answer when the time comes. Meanwhile, you are to be teamed with Ashe, who will see to putting you through the course."

It was a big hunk to swallow, but once down, Ross found it digestible.

The training opened up a whole new world to him. Judo and wrestling were easy enough to absorb, and he thoroughly enjoyed the workouts. But the patient hours of archery practice, the strict instruction in the use of a long-bladed bronze dagger were more demanding. The mastering of one new language and then another, the intensive drill in unfamiliar social customs, the memorizing of strict taboos and ethics were difficult. Ross learned to keep records in knots on hide thongs and was inducted into the art of primitive bargaining and trade. He came to understand the worth of a cross-shaped tin ingot compared to a string of amber beads and some well-cured white furs. He now understood why he had been shown a traders' caravan during that first encounter with the purpose behind Operation Retrograde.

During the training days his feeling toward Ashe changed materially. A man could not work so closely with another and continue to resent his att.i.tude; either he blew up entirely, or he learned to adjust. His awe at Ashe's vast amount of practical knowledge, freely offered to serve his own blundering ignorance, created a respect for the man which might have become friendship, had Ashe ever relaxed his own shield of impersonal efficiency. Ross did not try to breach the barrier between them mainly because he was sure that the reason for it was the fact that he was a "volunteer." It gave him an odd new feeling he avoided trying to a.n.a.lyze. He had always had a kind of pride in his record; now he had begun to wish sometimes that it was a record of a different type.

Men came and went. Hodaki and his partner disappeared, as did Jansen and his. One lost track of time within that underground warren which was the base. Ross gradually discovered that the whole establishment covered a large area under an external crust of ice and snow. There were laboratories, a well-appointed hospital, armories which stocked weapons usually seen only in museums, but which here were free of any signs of age, and ready for use. There were libraries with mile upon mile of tape recordings as well as films. Ross could not understand everything he heard and saw, but he soaked up all he could so that once or twice, when drifting off to sleep at night, he thought of himself as a sponge which had nearly reached its total limit of absorption.

He learned to wear naturally the clumsy kilt-tunic he had seen on the wolf slayer, to shave with practiced a.s.surance, using a leaf-shaped bronze razor, to eat strange food until he relished the taste. Making lesson time serve a double duty, he lay under sunlamps while listening to tape recordings, until his skin darkened to a weathered hue resembling Ashe's. There was always talk to listen to, important talk which he was afraid to miss.

"Bronze." Ashe weighed a dagger in his hand one day. Its hilt, made of dark horn studded with an intricate pattern of tiny golden nail heads, had a gleam not unlike that of the blade. "Do you know, Murdock, that bronze can be tougher than steel? If it wasn't that iron is so much more plentiful and easier to work, we might never have come out of the Bronze Age? Iron is cheaper and easier found, and when the first smith learned to work it, an end came to one way of life, a beginning to another.

"Yes, bronze is important to us here, and so are the men who worked it.

Smiths were sacred in the old days. We know that they made a secret of their trade which overrode the bounds of district, tribe, and race. A smith was welcome in any village, his person safe on the road. In fact, the roads themselves were under the protection of the G.o.ds; there was peace on them for all wayfarers. The land was wide then, and it was empty. The tribes were few and small, and there was plenty of room for the hunter, the farmer, the trader. Life was not such a scramble of man against man, but rather of man against nature----"

"No wars?" asked Ross. "Then why the bow-and-dagger drill?"

"Wars were small affairs, disputes between family clans or tribes. As for the bow, there were formidable things in the forests--giant animals, wolves, wild boars----"

"Cave bears?"

Ashe sighed with weary patience. "Get it through your head, Murdock, that history is much longer than you seem to think. Cave bears and the use of bronze weapons do not overlap. No, you will have to go back maybe several thousand years earlier and then hunt your bear with a flint-tipped spear in your hand if you are fool enough to try it."

"Or take a rifle with you." Ross made a suggestion he had longed to voice for some time.

Ashe rounded on him swiftly, and Ross knew him well enough now to realize that he was seriously displeased.

"That is just what you don't do, Murdock, not from this base, as you well know by now. You take no weapon from here which is not designed for the period in which your run lies. Just as you do not become embroiled while on that run in any action which might influence the course of history."

Ross went on polishing the blade he held. "What would happen if someone did break that rule?"

Ashe put down the dagger he had been playing with. "We don't know--we just don't know. So far we have operated in the fringe territory, keeping away from any district with a history which we can trace accurately. Maybe some day--" his eyes were on a wall of weapon racks he plainly did not see--"maybe some day we can stand and watch the rise of the pyramids, witness the march of Alexander's armies.... But not yet.

We stay away from history, and we are sure that the Reds are doing the same. It has become the old problem once presented by the atom bomb.

n.o.body wants to upset the balance and take the consequences. Let us find their outpost and we'll withdraw our men from all the other runs at once."

"What makes everyone so sure that they have an outpost somewhere?

Couldn't they be working right at the main source, sir?"

"They could, but for some reason they are not. As for how we know that much, it's information received." Ashe smiled thinly. "No, the source is much farther back in time than their halfway post. But if we find that, then we can trail them. So we plant men in suitable eras and hope for the best. That's a good weapon you have there, Murdock. Are you willing to wear it in earnest?"

The inflection in that question caught Ross's full attention. His gray eyes met those blue ones. This was it--at long last.

"Right away?"

Ashe picked up a belt of bronze plates strung together with chains, a twin to that Ross had seen worn by the wolf slayer. He held it out to the younger man. "You can take your trial run any time--tomorrow."

Ross drew a deeper breath. "Where--to when?"

"An island which will later be Britain. When? About two thousand B.C.

Beaker traders were beginning to open their stations there. This is your graduation exercise, Murdock."