"I not try to be bigger. Why you say you do not fall?"

"I do not fall!" howled Adam. "I do not fall, you stupid Brute!"

Goat held up a stern hand, enforcing silence.

"I can't certainly settle this disagreement, but I'd be inclined to accept what Brute says," said Goat thoughtfully. "You're smart enough to lie, Adam. Brute isn't. The only thing I can do is to run the experiment over. You shall go out again tomorrow, and this time I'll go with you."

"You'll see, father," said Adam confidently. "Adam will not fall."

"Perhaps not. But I must be sure. As much as I prefer your more human characteristics, Adam, it's entirely possible that Brute has some survival qualities that you lack."

"Is true, father," said Brute eagerly. "Some things kill Adam, they not kill Brute."

"You lie!" cried Adam again, turning on him. "Why do you lie, Brute?"

"No lie," insisted Brute. "You know, is true."

"Lie! Lie!" shouted Adam. "Adam is bigger and stronger! What do you say can kill Adam that does not kill Brute?"

"This," replied Brute calmly.

With an unhurried lunge, he picked up a heavy knife from Goat's desk. In a single easy movement, he turned and slashed Adam's throat neatly.

Choking and gurgling, Adam sank to his knees, bright blood spouting from his neck, while Goat stood frozen in horror. Adam fell prone, he kicked and threshed convulsively like a beheaded chicken, then twitched and lay still in a spreading pool of blood.

Brute calmly wiped the knife on his naked thigh and laid it back on the desk.

"Adam dead," he said without emotion. "Brute not lie."

Dismayed fury erupted through Goat's veins and a red haze swept over his eyes.

"You idiot!" he squawked. "So that won't kill you?"

Goaded beyond endurance, Goat seized the knife and swung it as hard as he could against Brute's neck. It thunked like an ax biting into a tree trunk, biting halfway through the flesh. Brute recoiled at the impact, tearing the handle from Goat's feeble hands and leaving the knife blade stuck in his throat.

Brute staggered momentarily. Then he reached up and jerked the knife away. Blood spurted through his severed throat. Brute clapped a hand to the wound, tightly.

For a moment, blood oozed through his fingers. Then, pale but steady, Brute dropped his hand.

The wound had closed! Its edges already were sealed, leaving a raw, red scar that no longer bled.

"Brute not lie," said Brute, the words forced out with some difficulty. "It not kill Brute."

Stunned by astonishment and disbelief, Goat stared at him, his mouth moving soundlessly.

"Go away," he whispered hoarsely at last. "Go out of here, monster!"

Obediently, Brute shambled out of the study. As he passed through the door, Goat regained his voice and called after him:

"Tell the children to come and take away Adam's body."

Kilometers away, Maya Cara Nome and S. Nuwell Eli rode a groundcar that moved swiftly across the interminable waves of the red sand. It swayed through hollows and jounced over multiple ridges, Nuwell steering it with some difficulty. In the steely sky, the small sun moved downward, its brightness unimpaired by the occasional thin clouds which moved before it.

The sun touched the western horizon, seemed to hesitate, dropped with breathtaking suddenness, and the stars immediately began to appear in the deepening twilight sky.

They stopped and had a compact meal, heated in the groundcar's short-wave cooker. Then Nuwell switched on the headlights and they went on again.

Soon afterward, a faint spot of light appeared in the desert far ahead of them. As they approached it, it became a yellow-lighted window in a huge black mass rearing up against the night sky. They had reached Ultra Vires.

Nuwell announced their arrival over the groundcar radio and swung the groundcar up beside the building's main entrance. He sealed the groundcar's door to the building air-lock so they would not have to don marsuits.

After a few moments, the airlock opened. They passed through it and were greeted by a skinny, shriveled little man with watery blue eyes and a goatee.

"I was expecting you, but not tonight," said this person, rather sourly. "Well, come on in and I'll have the children fix you something to eat if you haven't eaten."

"I'm S. Nuwell Eli," said Nuwell, holding out a hand which the other ignored. "This is the terrestrial agent, Miss Maya Cara Nome. You are Dr. Hennessey, I assume."

"That's right," said Goat. "Do you want supper?"

"No, thank you, we ate on the way," said Nuwell. "I'd like to get started with the inspection as soon as possible."

"Inspection or investigation?" suggested Goat, sniffling. "Well, no matter. I have nothing to hide."

He led them down a dim, dusty corridor, stretching deep into the dark bowels of the building, and turned aside into a paper-stacked room which evidently was his study. He went straight to a big desk, sat down, swivelled his chair around and waved them to seats. Nuwell shuffled a little uncomfortably, then sank into a chair, but Maya remained standing by the door, her small traveling bag in her hand, indignation rising in her.

"Before you settle down to charts and questions, Dr. Hennessey, do you mind showing us to our rooms so we may wash away some of the travel dust?" she asked icily, black eyes snapping.

At this, Goat jumped to his feet, sincere contrition in his face wiping out all traces of his irritated gruffness.

"I'm very sorry!" he exclaimed. "I hope you will forgive my manners, but I've lived and worked here alone in the desert so long that I had forgotten the niceties of civilization."

This apology cleared the air. Goat showed them their overnight quarters, adjoining rooms which were not luxurious but were reasonably comfortable, and after a time the three of them congregated once more in Goat's study, all of them in better humor.

"Let us have some wine first," suggested Goat. "This is very good red wine, imported from Earth."

He went to the door and shouted into the corridor.

"Petway!"

Goat returned to his chair. A few moments later, a twittering noise sounded in the corridor, then a horrible little apparition appeared in the door. It was a child-sized creature, naked, grotesquely barrel-chested and teetering on thin, twisted legs. Its hairless head was skull-like, with gaping mouth and huge, round eyes.

Maya gasped, profoundly shocked. The little creature looked more like a miniature Martian native than a human, but the Martians themselves were not so distorted. She saw her own shock reflected in Nuwell's face.

"Petway, get us three glasses of wine," commanded Goat calmly.

Petway vanished and Goat turned briskly back to his guests.

"Now," he said, "I shall outline the progress of my experiments to you and answer any questions you may have."

3

Maya's education was extensive, but it did not include the genetic sciences. She was able to follow Goat's explanations and his references to the charts he hung, one after another, on the wall of his study, but she was able to follow them only in a general sense. The technical details escaped her.

Nuwell seemed to have a better grasp of the subject. He nodded his dark, curly head frequently, and occasionally asked a question or two.

"Surgery is performed with a concentrated electron stream on the cells of the early embryo," said Goat. "I call it surgery, but actually it is an alteration of the structure of certain specific genes which govern the characteristics I am attempting to change. Such changes would, of course, then be transmitted on down to any