“Yes, but there are millions of cancer cells all over. It would take how long to get them, one by one?”

“Not quite necessarily one by one, Tertia,” said Johannes. “Even though the cancer is widespread, it exists in clumps. Mike is equipped to burn off and close capillaries leading to the clump, and a million cells could die at a stroke in that fashion. He will only occasionally have to deal with cells on an individual basis.”

“Still, how long would it take?”

Johannes’s youngish face went into a grimace as though it were difficult to decide what to say. “It could take hours, Tertia, if we’re to do a thorough job. I admit that.”

“And every moment of those hours will increase the chance of reexpansion.”

Mike said, “Mrs. Arnfeld, I will labor to prevent reexpansion.”

Mrs. Arnfeld turned to the robot and said earnestly, “Can you, Mike? I mean, is it possible for you to prevent it?”

“Not entirely, Mrs. Arnfeld. By monitoring my size and making an effort to keep it constant, I can minimize the random changes that might lead to a reexpansion. Naturally, it is almost impossible to do this when I am actually reexpanding under controlled conditions.”

“Yes, I know. My husband has told me that reexpansion is the most dangerous time. But you will try, Mike? Please?”

“The laws of robotics ensure that I will, Mrs. Arnfeld,” said Mike solemnly.

As they left, Johannes said in what Mrs. Arnfeld understood to be an attempt at reassurance, “Really, Tertia, we have a holo-sonogram and a detailed cat scan of the area. Mike knows the precise location of every significant cancerous lesion. Most of his time will be spent searching for small lesions undetectable by instruments, but that can’t be helped. We must get them all, if we can, you see, and that takes time. Mike is strictly instructed, however, as to how small to get, and he will get no smaller, you can be sure. A robot must obey orders.”

“And the reexpansion, Ben?”

“There, Tertia, we’re in the lap of the quanta. There is no way of predicting, but there is a more than reasonable chance that he will get out without trouble. Naturally, we will have him reexpand within Gregory’s body as little as possible-just enough to make us reasonably certain we can find and extract him. He will then be rushed to the safe room where the rest of the reexpansion will take place. Please, Tertia, even ordinary medical procedures have their risk.”

Mrs. Arnfeld was in the observation room as the miniaturization of Mike took place. So were the holovision cameras and selected media representatives. The importance of the medical experiment made it impossible to prevent that, but Mrs. Arnfeld was in a niche with only Johannes for company, and it was understood that she was not to be approached for comment, particularly if anything untoward occurred.

Untoward! A full and sudden reexpansion would blow up the entire operating room and kill every person in it. It was not for nothing the observation room was underground and half a mile away from the viewing room.

It gave Mrs. Arnfeld a somewhat grisly sense of assurance that the three miniaturists who were working on the procedure (so calmly, it would seem-so calmly) were condemned to death as firmly as her husband was in case of-anything untoward. Surely, she could rely on them protecting their own lives to the extreme; they would not, therefore, be cavalier in the protection of her husband.

Eventually, of course, if the procedure were successful, ways would be worked out to perform it in automated fashion, and only the patient would be at risk. Then, perhaps, the patient might be more easily sacrificed through carelessness-but not now, not now. Mrs. Arnfeld keenly watched the three, working under imminent sentence of death for any sign of discomposure.

She watched the miniaturization procedure (she had seen it before) and saw Mike grow smaller and disappear. She watched the elaborate procedure that injected him into the proper place in her husband’s body. (It had been explained to her that it would have been prohibitively expensive to inject human beings in a submarine device instead. Mike, at least, needed no life-support system.)

Then matters shifted to the screen, in which the appropriate section of the body was shown in holosonogram. It was a three-dimensional representation, cloudy and unfocused, made imprecise through a combination of the finite size of the sound waves and the effects of Brownian motion. It showed Mike dimly and noiselessly making his way through Gregory Arnfeld’s tissues by way of his bloodstream. It was almost impossible to tell what he was doing, but Johannes described the events to her in a low, satisfied manner, until she could listen to him no more and asked to be led away.

She had been mildly sedated, and she had slept until evening, when Johannes came to see her. She had not been long awake and it took her a moment to gather her faculties. Then she said, in sudden and overwhelming fear, “What has happened?”

Johannes said, hastily, “Success, Tertia. Complete success. Your husband is cured. We can’t stop the cancer from recurring, but for now he is cured.”

She fell back in relief. “Oh, wonderful.”

“Just the same, something unexpected has happened and this will have to be explained to Gregory. We felt that it would be best if you did the explaining. ‘,

“I?” Then, in a renewed access of fear, “What has happened?” Johannes told her.

It was two days before she could see her husband for more than a moment or two. He was sitting up in bed, looking a little pale, but smiling at her.

“A new lease on life, Tertia,” he said buoyantly.

“Indeed, Greg, I was quite wrong. The experiment succeeded and they tell me they can’t find a trace of cancer in you.”

“Well, we can’t be too confident about that. There may be a cancerous cell here and there, but perhaps my immune system will handle it, especially with the proper medication, and if it ever builds up again, which might well take years, we’ll call on Mike again.”

At this point, he frowned and said, “You know, I haven’t seen Mike.”

Mrs. Arnfeld maintained a discreet silence.

Arnfeld said, “They’ve been putting me off.”

“You’ve been weak, dear, and sedated. Mike was poking through your tissues and doing a little necessary destructive work here and there. Even with a successful operation you need time for recovery.”

“If I’ve recovered enough to see you, surely I’ve recovered enough to see Mike, at least long enough to thank him.”

“A robot doesn’t need to receive thanks.”

“Of course not, but I need to give it. Do me a favor, Tertia. Go out there and tell them I want Mike right away.”

Mrs. Arnfeld hesitated, then came to a decision. Waiting would make the task harder for everyone. She said carefully, “ Actually, dear, Mike is not available.”

“Not available! Why not?”

“He had to make a choice, you see. He had cleaned up your tissues marvelously well; he had done a magnificent job, everyone agrees; and then he had to undergo reexpansion. That was the risky part.”

“Yes, but here I am. Why are you making a long story out of it?”

“Mike decided to minimize the risk. “

“Naturally. What did he do?”

“Well, dear, he decided to make himself smaller. “

“What! He couldn’t. He was ordered not to.”

“That was Second Law, Greg. First Law took precedence. He wanted to make certain your life would be saved. He was equipped to control his own size, so he made himself smaller as rapidly as he could, and when he was far less massive than an electron he used his laser beam, which was by then too tiny to hurt anything in your body, and the recoil sent him flying away at nearly the speed of light. He exploded in outer space. The gamma rays were detected.”

Arnfeld stared at her. “You can’t mean it. Are you serious? Mike is dead?”