The Xanthe Desert stretched red and barren on all sides of the plodding couple, the sands unbroken by the form of plant or stone or any living thing, all the way to the tight horizon of Mars. Above them, the small, glittering sun slid down the copper-hued sky slowly toward the west.

It was remarkable, thought Maya, how smooth and flat the desert looked from the air, and how rough and rolling it was when one had to walk across the packed sand. They had been walking for hours and, despite the gentle gravity of Mars, she was getting very tired.

"It's farther than I thought," said Nuwell, his voice distorted by the marshelmet speaker. "Distances on the chart are deceptive. We may not reach Ultra Vires by night."

Maya did not answer. Again, as she had many weeks before, she was in the grip of a sensation that this desert through which they walked was only a surface thing, a shimmering mask to the reality which lay behind it. That reality seemed very deep, very significant, and she felt that she was on the verge of comprehending it, but could not quite grasp it.

She was a little irritated at Nuwell for speaking when he did. If his voice had not interrupted her probing emotions, she felt, she might have broken through to that reality she sensed.

"Nuwell," she said, giving it up, "I'm going to have to rest a while. If we don't make it by night, we don't make it. There's always tomorrow, and I'm tired."

Reluctantly, he consented, and they sat down together on the sand. Nuwell pulled a chart out of his marsuit pocket and began to study it. Maya lay back, clasped her hands behind her helmet and closed her eyes, gratefully feeling the tired muscles relax and the perspiration that bathed her begin to dissolve in the gentle circulation of the marsuit's temperature-control system.

"Maya!" exclaimed Nuwell suddenly. "Look! We're going to be rescued!"

She sat up and looked in the direction of his pointing finger. On the horizon to the northeast was a cloud of dust, too placid and stationary to be a sandstorm.

They stood up, and Nuwell spoke hastily into his helmet radio on the conventional emergency band.

"Attention, groundcar! Attention, groundcar! We're afoot and in trouble. We're afoot, due southwest from your position. Help, please. Attention, groundcar!"

There was no radio reply in the ensuing silence. But all at once it was as though a deep and alien voice spoke within the depths of Maya's mind:

"We see you."

Startled, she looked curiously at Nuwell. But he evidently had not had the same experience. He was chattering into the radio frantically again.

"They're evidently not tuned in on the emergency band, Nuwell," she said to him. "But they're coming almost directly toward us. They're bound to see us soon, if they haven't already."

"That's true," said Nuwell, and added sourly: "But they ought to be tuned in. It's required by law."

The dustcloud moved closer slowly, too slowly for a groundcar. They were able to discern a dark nucleus below and in front of it. Then Nuwell said:

"In the name of space! It isn't a groundcar, Maya. It's a band of Martians! Let's get out of here!"

He started to walk on swiftly, but Maya stood her ground.

"Don't be silly," she said. "Martians won't hurt us. I was raised among them."

Nuwell stopped and returned reluctantly to her side.

"They may not hurt us, but why wait for them?" he demanded, and there was a touch of hysterical fright to his tone. "Let's go on, Maya!"

"We may very well have gotten off course in trying to go straight to Ultra Vires," replied Maya logically. "That may be why we've not sighted it yet. The Martians will know where it is, and meeting them may prevent us from getting lost in the desert."

Nuwell subsided, but she could see from the expression on his face that he was in a blue funk. This puzzled her. She could not understand why anyone would be afraid of Martians. They were huge, and ugly, and alien, but they were not inimical to humans.

When the Martians came near enough, Maya waved her arms at them and started off to meet them, Nuwell following her at a little distance. The Martians changed course slightly and came toward them.

Maya called childhood memories to her aid. She turned her helmet speaker to its maximum volume, and spoke to them in their own language, in the deepest tones possible to her.

"Children of the past, we seek that place in the desert which is called 'Ultra Vires' by humans," she said. "Can you show us the direction in which we must travel?"

The Martians gathered around her, towering over her. There were four of them. Their huge chests moved slowly, mixing oxygen from their great humps with the surrounding air. Their thin arms hung limp at their sides, and their big ears were pricked forward toward her. Their huge, dark eyes seemed to look through her and beyond her.

"The sun moves toward this place, but there are no humans there now," boomed one of the Martians. "Nothing lives there now except small animals in the walls and corridors."

"This we know," answered Maya. "We wish to go there that we may communicate with other humans and have them come and get us."

She wanted to say that the supplies of oxygen in their marsuit tanks were inadequate to take them anywhere other than Ultra Vires, but she did not know how to say this properly in the Martian language.

But, to her astonishment, the Martian answered as though she had said it.

"If the breathing chemicals which you carry are at such a depleted stage, you cannot chance going astray," said the creature. "Rather than tell you the direction of this place, we shall accompany you there."

Throughout this conversation, Nuwell had been standing at Maya's side, his face bearing an expression of mingled curiosity, irritation and awe. Maya turned to him.

"The Martians say they will go with us to Ultra Vires, so we won't get lost," she told him.

"No!" he exclaimed vehemently. "Tell them we don't want them along. Tell them just to show us the way, and we'll go alone."

"Don't be ridiculous," replied Maya coldly, and indicated to the Martian that they were ready to accompany the group.

They moved off together toward the west, the four Martians and the two humans. Maya, feeling somewhat relieved that now they had expert help in reaching their goal, attempted to talk to Nuwell, but he refused to answer except in monosyllables. He was angry that she had agreed for the Martians to accompany them, and obviously was still very nervous at their presence.

So she talked instead with the Martian who had acted as spokesman for the group. Its name, she learned, was Qril.

"The place to which you go lies under an evil atmosphere," said Qril. "The human who abode there many years attempted to do things wrongly."

"We were there in the season before this one," answered Maya. "This was just before that human left."

"I already had read this in you," said Qril. "I also read in you that, as a child, you lived among us who are children of the past. Therefore, perhaps you knew before I spoke that an evil atmosphere remains at this place and has not yet been washed away by time."

"No, I was not taught such matters as a child," answered Maya. "But tell me, it is true that this man tried to do evil things, by human standards, but were Goat Hennessey's genetic experiments also evil by Martian standards?"

"You do not read what I have said quite correctly," replied Qril. "The evil atmosphere is left by the man, because what he did was evil by his own standards. I said only that he attempted to do things wrongly."

"What do you mean?" asked Maya.

"To explain to you, I must speak to you about things about which you already know partially," answered Qril. "Before you were born, the human you call Goat was one of a group of humans who sought ways to make humans independent of the spaceships which bring materials from Earth to Mars and create small islands of terrestrial conditions in the midst of the Martian environment. When they met the natural resistance of those humans who gain material advantage through operation of the spaceships, they came into the desert to be free to work.

"Seeking to get far from the men who resisted their work, this group of humans went to that area which you know as the Icaria Desert. Some of us who are children of the past live at that place sometimes, and these humans sought our help, knowing that we possess many remnants of the knowledge that our forefathers had.

"But we had difficulty helping them. They were attempting to follow two courses simultaneously, and both of them were wrong."

"I know something of those two courses," said Maya. "Some of them were trying to develop human extrasensory powers so that materials could be teleported from Earth, and the others were trying to change the human body physiologically so that humans could live under Martian conditions. But you say they were both wrong?"

"In each way that they followed, they sought to make humans partly like us, the children of the past," said Qril. "We have the power to communicate with our minds over a distance, and some of us are able to transport things with our minds over a distance. We do not need your rich terrestrial air, because we take oxygen directly from the soil and store it in our bodies for combustion purposes.

"But humans and the children of the past are different forms of life, and they cannot be made so much alike. It is possible for humans to develop mental powers similar to ours, but this course would leave them dependent upon importing materials from Earth, even though this would be by mind transmission instead of by spaceship. The other course they followed could not succeed, because the human body cannot be altered so that it is able to take oxygen from the soil and store it for later use."

"But you're wrong!" exclaimed Maya. "Goat Hennessey had succeeded in developing some humans who could live without oxygen in the air for a time. His experiments were imperfect, it's true, but they were able to do that."

"The imperfect humans that the human called Goat had developed were not what he thought," replied Qril. "We tried to help the humans to find the right course, but they could not understand us well. We tried to show them, by charts and example, that the proper way to adapt a human to Martian conditions was a different way.

"Because Earth is nearer the Sun, humans have a possibility that we do not have. What we tried to show these humans was a method whereby they could change the embryonic physiology so that the adult human would be able to use the energy of solar radiations directly, instead of depending on the energy of combustion of those chemicals you call oxygen and carbon. This makes the body independent of both air and food, and has the advantage also of giving a far superior regenerative power to the bodily tissues.

"The human, Goat, for reasons that are not known, stole some of our charts and two of the pregnant female humans, and continued his work at this place to which we are going. But he thought he was still attempting to change the physiology so that oxygen could be stored, and therefore his experiments went wrongly."

"But he had your charts," objected Maya. "Even though he was not making the alterations he thought he was, how could he go wrong if he followed the charts?"

"The charts showed the changes to be made in the embryonic cells, but they could not show the method whereby the changes are made," replied Qril. "The human, Goat, attempted to make these changes by mechanical, surgical methods but these are too crude to be successful. The method we utilize to make such changes, which is the only right method, is to focus the mental forces upon the embryo. I believe you would call it psychokinesis."

Maya was vastly excited at this revelation.

"Then Goat's oldest experiments, the ones he called Brute and Adam, were actually the ones on whom you children of the past had performed the embryonic changes!" she exclaimed. "They must have been the sons of the pregnant women he kidnapped. That's why they were more successful than the others!"

"That is true," said Qril. "We had completed the change on only one of the two, therefore only that one would develop into an adult who could live in complete independence of air and food, if necessary. The other one would never be able to do it for more than a short period without returning to terrestrial conditions."

The party now came over a long low ridge, and the mass of Ultra Vires rose from the desert ahead of them. The sun was near setting, and the black walls of the stronghold huddled sullenly under its crimson rays.

The Martians left them here, and Nuwell and Maya went on alone toward their goal. Nuwell expelled an audible sigh of relief.

"I'm glad we're free of those monsters," he said. "I don't understand how you could carry on a conversation with such creatures, Maya. It sounded like a series of animal grunts and cries to me. I caught an occasional word, like 'oxygen' and 'psychokinesis.' What were you talking about?"

"He was telling me about Goat Hennessey's experiments, and how they differed from the rebels' experiments before Goat came to Ultra Vires," answered Maya.

"That kind of talk serves no good purpose," said Nuwell irritably. "The rebel movement has been broken now, and there's no point in thinking about the illegal things they tried to do."

They came down the slope and approached the southern airlock of Ultra Vires. The airlock was still sealed. Nuwell activated it, and they went through it into the big building.

It was dark inside. Nuwell fumbled around a wall and found a light switch. He pressed it, but nothing happened.

"The electrical system isn't operating," he said. "We'll have to use our marsuit torches."

He switched on his flashlight. It cast a long beam down the dusty corridor. Far ahead of them, a small animal scurried across the faint light and vanished into the darkness.

Nuwell checked his atmosphere dial.

"The oxygen in here is all right," he said. "The air has been maintained, anyhow. We can take off our helmets."

They took off the marshelmets and walked down the corridor. They checked each side door, looking for the communications room, but found only empty chambers or abandoned rooms in which books, papers and broken furniture were scattered in complete disorganization.

It took them nearly an hour to find the communications room. And there they met disappointment.

Ultra Vires' radio transmitter and receiver had been dismantled. There was nothing there but a jumble of broken tubes, discarded parts and bare wire ends dangling from the walls. Nothing but an overturned table and two bent metal chairs.

"That settles that," said Nuwell, more philosophically then Maya would have expected. "Our only hope is to find a groundcar."

That necessitated another search, but at last they found the motor pool. And there were three groundcars, all in various stages of breakdown or dismantlement.

"It looks like we'll have to walk, Nuwell," said Maya.

Nuwell shook his head.

"I checked the chart carefully," he said. "The oxygen supply of a marsuit won't take us either back to the Canfell Farm or to Ophir, even with extra tanks. We're just going to have to cannibalize two of these machines and repair us a groundcar."

"But, Nuwell, how long will that take?"

"I don't know," he admitted. "It looks like it may be quite a job. I expect it will take two or three weeks, but that's the only way we're going to get out of here."

He looked at her speculatively.

"It's a shame we aren't already married," he said. "This would provide us with a honeymoon, of a sort, out here by ourselves in the desert."

"Well, we aren't," she said flatly. "And we won't be until we get back to Mars City."

"That's true," he said. "Well, the only thing we can do for tonight is to have supper and find the rooms that Goat assigned us when we were here before. I hope he left some beds intact in those, or some of the other rooms. If not, we may have some uncomfortable nights ahead of us."

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