He thought, They've got to her.

He might snatch her out of the doorway. They would run, try to make it to safety. But how could they? The visitor would be standing in the shadows of the hallway. It would be a sinister man, he imagined, with a thick, brutal voice, and foreign accent, standing there with a hand in his jacket pocket and a bulge there that was bigger than his hand.

Numbly he stepped inside.

“In the living room,” said Mercedes. A smile flashed momentarily across her face. “I think it's all right.”

The visitor was standing. He had an unreal look about him, the unreality of perfection. His face and body were flawless and carefully devoid of individuality. He might have stepped off a billboard.

His voice had the cultured and unimpassioned sound of the professional radio announcer. It was entirely free of accent.

He said, “It was quite troublesome getting you home, Dr. Johannison.”

Johannison said, “Whatever it is, whatever you want, I’m not cooperating.”

Mercedes broke in. “No, Alex, you don't understand. We've been talking. He says all radioactivity has been stopped.”

“Yes, it has, and how I wish this collar-ad could tellme how it was done! Look here, you, are you an American?”

“You still don't understand, Alex,” said his wife. “It's stopped all over the world. This man isn't from anywhere on Earth. Don't look at me like that, Alex. It's true. I know it's true. Look at him.”

The visitor smiled. It was a perfect smile. He said, “This body in which I appear is carefully built up according to specification, but it is only matter. It's under complete control.” He held out a hand and the skin vanished. The muscles, the straight tendons, and crooked veins were exposed. The walls of the veins disappeared and blood flowed smoothly without the necessity of containment. All dissolved to the appearance of smooth gray bone. That went also.

Then all reappeared.

Johannison muttered, “Hypnotism!”

“Not at all,” said the visitor, calmly.

Johannison said, “Where are you from?”

The visitor said, “That's hard to explain. Does it matter?”

“I've got to understand what's going on,” cried Johannison. “Can't you see that?”

“Yes, I can. It's why I'm here. At this moment I am speaking to a hundred and more of your people all over your planet. In different bodies, of course, since different segments of your people have different preferences and standards as far as bodily appearance is concerned!”

Fleetingly, Johannison wondered if he was mad after all. He said, “ Are you from-from Mars? Any place like that? Are you taking over? Is this war?”

“You see,” said the visitor, “that sort of attitude is what we're trying to correct. Your people are sick, Dr. Johannison, very sick. For tens of thousands of your years we have known that your particular species has great possibilities. It has been a great disappointment to us that your development has taken a pathological pathway. Definitely pathological.” He shook his head.

Mercedes interrupted, “He told me before you came that he was trying to cure us.”

“Who asked him?” muttered Johannison. The visitor only smiled. He said, “I was assigned the job a long time ago, but such illnesses are always hard to treat. For one thing, there is the difficulty in communication.”

“We're communicating,” said Johannison stubbornly. “Yes. In a manner of speaking, we are. I'm using your concepts, your code system. It's quite inadequate. I couldn't even explain to you the true nature of the disaster of your species. By your concepts, the closest approach I can make is that it is a disease of the spirit.”

“Huh.”

“It's a kind of social ailment that is very ticklish to handle. That's why I've hesitated for so long to attempt a direct cure. It would be sad if, through accident, so gifted a potentiality as that of your race were lost to us. What I've tried to do for millennia has been to work indirectly through the few individuals in each generation who had natural immunity to the disease. Philosophers, moralists, warriors, and politicians. All those who had a glimpse of world brotherhood. All those who-”

“All right. You failed. Let it go at that. Now suppose you tell me about your people, not mine.”

“What can I tell you that you would understand?”

“Where are you from? Begin with that.”

“You have no proper concept. I'm not from anywhere in the yard.”

“What yard?”

“In the universe, I mean. I'm from outside the universe.”

Mercedes interrupted again, leaning forward. “ Alex, don't you see what he means? Suppose you landed on the New Guinea coast and talked to some natives through television somehow. I mean to natives who had never seen or heard of anyone outside their tribe. Could you explain how television worked or how it made it possible for you to speak to many men in many places at once? Could you explain that the image wasn't you yourself but merely an illusion that you could make disappear and reappear? You couldn't even explain where you came from if all the universe they knew was their own island.”

“Well, then, we're savages to him. Is that it?” demanded Johannison.

The visitor said, “Your wife is being metaphorical. Let me finish. I can no longer try to encourage your society to cure itself. The disease has progressed too far. I am going to have to alter the temperamental makeup of the race.”

“How?”

“There are neither words nor concepts to explain that either. You must see that our control of physical matter is extensive. It was quite simple to stop all radioactivity. It was a little more difficult to see to it that all things, including books, now suited a world in which radioactivity did not exist. It was still more difficult, and took more time, to wipe out all thought of radioactivity from the minds of men. Right now, uranium does not exist on Earth. No one ever heard of it.”

“I have,” said Johannison. “How about you, Mercy?”

“I remember, too,” said Mercedes.

“You two are omitted for a reason,” said the visitor, ''as are over a hundred others, men and women, all over the world.”

“No radioactivity,” muttered Johannison. “Forever?”

“For five of your years,” said the visitor. “It is a pause, nothing more. Merely a pause, or call it a period of anesthesia, so that I can operate on the species without the interim danger of atomic war. In five years the phenomenon of radioactivity will return, together with all the uranium and thorium that currently do not exist. The knowledge will not return, however. That is where you will come in. You and the others like you. You will re-educate the world gradually.”

“That's quite a job. It took fifty years to get us to this point. Even allowing for less the second time, why not simply restore knowledge? You can do that, can't you?”

“The operation,” said the visitor, “will be a serious one. It will take anywhere up to a decade to make certain there are no complications. So we want re-education slowly, on purpose.”

Johannison said, “How do we know when the time comes? I mean when the operation's over.”

The visitor smiled. “When the time comes, you will know. Be assured of that.”

“Well, it's a hell of a thing, waiting five years for a gong to ring in your head. What if it never comes? What if your operation isn't successful?”

The visitor said seriously, “Let us hope that it is.”

“But if it isn't? Can't you clear our minds temporarily, too? Can't you let us live normally till it's time?”

“No. I'm sorry. I need your minds untouched. If the operation is a failure, if the cure does not work out, I will need a small reservoir of normal, untouched minds out of which to bring about the growth of a new population on this planet on whom a new variety of cure may be attempted. At all costs, your species must be preserved. It is valuable to us. It is why I am spending so much time trying to explain the situation to you. If I had left you as you were an hour ago, five days, let alone five years, would have completely ruined you.”