They unfastened their helmets and lifted them off. The air was sharp and tangy, the room was warm.

"That's better," said Caroline.

"Chairs?" asked the old man, pointing out a couple.

They sat and he lowered his old body into another.

"Well, well," he said, and his thoughts had a grandfatherly touch about them, "humans of an earlier age. Splendid physical specimen, the two of you. And fairly barbaric still — but the stuff is in you. You use your mouths to talk with and man hasn't talked with other than his thoughts for thousands and thousands of years. That in itself would set you pretty far back."

"Pretty far is right," said Gary. "We are the first humans who ever left the solar system."

"That is far," said the old man. "Far, far…"

His sharp eyes watched them closely. "You must have an interesting story," be suggested.

"We have," said Caroline and swiftly they told it to him, excitedly, first one and then the other talking, adding in details, explaining situations, laying before him the problems which they faced.

He listened intently, snapping questions now and then, his bright old eyes shining with the love of adventure, the wrinkles in his face taking on a kind benevolence as if they might be children, home from the first day of school, telling of all the new wonders they had met.

"So you came to me," he said. "You came trundling down a crazy timepath to seek me out. So that I could tell you the things you need to know."

Caroline nodded. "You can tell us, can't you?" she asked. "It means so much to us — so much to everyone."

"I wouldn't worry," said the old man. "If the universe had come to an end, I wouldn't be here. You couldn't have come to me."

"But maybe you aren't real," said Caroline. "Maybe you are just a shadow. A probability…"

The oldster nodded and combed his beard with gnarled fingers. The breath wheezed in his mighty chest.

"You are right," he agreed. "I may be only a shadow. This world of mine may be no more than a shadow-world. I sometimes wonder if there is any reality at all — if there is anything but thought. Whether it may not be that some gigantic intelligence has dreamed all these things we see and believe in and accept as real… if the giant intelligence may not have set mighty dream stages and peopled them with actors of his imagination. I wonder at times if all the universes may be nothing more than a shadow show. A company of shadowy actors moving on a shadow stage."

"But you can tell us," pleaded Caroline. "You will tell…"

His old eyes twinkled. "I will tell you, yes, and gladly. Your fifth dimension is eternity. It is everything and nothing… all rolled into one. It is a place where nothing has ever happened and yet, in a sense, where everything has happened. It is the beginning and the end of all things. In it there is no such thing as space or time or any other phenomena which we attribute to the four-dimensional continuum."

"I can't understand," said Caroline, lines of puzzlement twisting her face. "It seems so hopeless, so entirely hopeless. Can it be explained by mathematics?"

"Yes," said the old man, "but I'm afraid you wouldn't understand. The mathematics necessary to explain it weren't evolved until just a few thousand years ago."

He stroked the beard down smoothly over his pouter-pigeon chest.

"I do not wish to make you feel badly," he declared, "but I can't see how you would have the intelligence to grasp it. After all, you are a people from an earlier age, an almost barbaric age."

"Try her," growled Gary.

"All right," said the old man, but there was a patronizing tone to his thoughts.

Gary gained a confused impression of horrific equations, of bracketed symbols that built themselves into a tangled and utterly confused structure of meaning — a meaning that seemed so vast and all-inclusive that his mind instinctively shuddered away from it.

Then the thoughts were gone and Gary's mind was spinning with them, with the vital forcefulness that he had guessed and glimpsed behind the symbolic structure that had been in the mathematics.

He looked at Caroline and saw that she was puzzled. But suddenly a look of awe spread over her face.

"Why," she said, and hesitated slightly, "…. why, the equations cancel, represent both everything and nothing, both zero and the ultimate in everything imaginable."

Gary caught a sense of surprise and confusion that flashed through the mind of their host.

"You understand," said the faltering thought. "You grasp the meaning perfectly."

"Didn't I tell you," said Gary. "Of course, she understands."

"

Caroline was talking, almost as if she were talking to herself, talking her thoughts aloud. "That means the energy would be timeless. It would have no time factor, and since time is a factor in power, its power would be almost infinite. There'd be no stopping it, once it started."

"You are right," said the old man. "It would be raw, created energy from a region where four-dimensional laws are no longer valid. It would be timeless and formless."

"Formless," said Caroline. "Of course, it would be formless. It wouldn't be light, or heat, or matter, or motion, or any other form of energy such as we know. But it could be anything. It would be waiting to become something. It could crystallize into anything."

"Good Lord," said Gary, "how could you handle stuff like that? Your hyperspheres wouldn't handle it. It could mold space itself. It could annihilate time."

Caroline looked at him soberly.

"If I could create a fifth-dimensional trap," she said, "if I could trap it in the framework of the medium from which it came. Don't you see that such a framework would attract it, would gather it in and hold it. Like a battery holds energy. Like water seeking its own level and coming to rest."

"Sure," agreed Gary, "if you could create a fifth-dimensional trap. But you can't. It's eternity. The dimension of eternity. You can't go fooling around with eternity."

"Yes, she can," said the old man.

The two of them stared at him, not believing.

"Listen closely," said the oldster. "By rotating a circle through three dimensions you create a sphere. Rotate the sphere through four dimensions and you have a hypersphere. You already have created this. You have bent time and space around a mass to create a hypersphere, a miniature universe. Now all you have to do is rotate the hypersphere through five-dimensional space."

"But you'd have to be in five-dimensional space to do that," objected Gary.

"No, you wouldn't," contended the old man. "Scattered throughout three-dimensional space are ether eddies and time faults and space traps — call them anything you like. They are a common phenomena and they're nothing more, when you come right down to it, than isolated bits of four-dimensional space scattered around through three-dimensional space. The same thing would apply to a fifth dimension in the fourth dimension."

"But how," asked Caroline, "would one go about it? How would one rotate a hypersphere through the fifth dimension?"

Again Gary had that sense of confusion as the thoughts of the ancient one swept over him, thoughts that translated themselves into symbols and equations and brackets of mathematics that it seemed impossible any man could know.

"Gary," gasped Caroline, "have you a pencil and some paper?"

Gary fumbled in his pocket and found an old envelope and a stub of pencil. He handed them to her.

"Please repeat that very slowly," she said, smiling at the old man.

Gary watched in amazement as Caroline, slowly and carefully, jotted down the formulas, equations, symbols — carefully checking and going over them, checking and rechecking so there could be no mistake.

"It will take power," she said. "Tremendous power. I wonder if the Engineers can supply it."