Dr. Cloyd paused. Mersey had no immediate reply.

The traveler made use of the silence to consider this plausible, but frightening theory. To accept the theory would be to accept a destiny of madness here on this world, although the doctor had been kind enough to draw a distinction between madness in one dimension and a mere lack of natural balance in another.

Mersey again seized upon the traveler's mind and spoke its thoughts.

But as he spoke, he voiced a conclusion which the traveler had not yet admitted even to himself.

"Then the answer is inescapable," Mersey said, his tone flat and unemotional. "It is theoretically possible for all of our people to migrate to this world and find refuge of a sort. But if we established ourselves in the minds of your normal people, we'd be without will. As mere observers, we'd become a.s.similated in time, and thus extinguished as a separate race. That, of course, we could not permit. And if we settled in the minds most suitable to receive us, we would be in the minds of those who by your standards are insane--whose destiny is controlled by the others. Here again we could permit no such fate.

"That alone would be enough to send me back to my people to report failure. But there is something more--something I don't think you will believe, for all your ability to synthesize acceptance of another viewpoint."

"And what is that?"

"First I must ask a question. In speaking to me now, do you still believe yourself to be addressing Mersey, your fellow human being, and humoring him in a delusion? Or do you think you are speaking through him to me, the inhabitant of another world who has borrowed his mind?"

The doctor smiled and took time to relight his pipe.

"Let me answer you in this way," he said. "If I were convinced that Mersey was merely harboring a delusion that he was inhabited by an alien being, I would accept that situation clinically. I would humor him, as you put it, in the hope that he'd be encouraged to talk freely and perhaps give me a clue to his delusion so I could help him lose it. I would speak to him--or to you, if that were his concept of himself--just as I am speaking now.

"On the other hand, if I were convinced by the many unusual nuances of our conversation that the mind I was addressing actually was that of an alien being--I would still talk to you as I am talking now."

The doctor smiled again. "I trust I have made my answer sufficiently unsatisfactory."

The visitor's reaction was spoken by Mersey. "On the contrary, you have unwittingly told me what I want to know. You'd want your answer to be satisfactory if you were speaking to Mersey, the lunatic. But because you'd take delight in disconcerting me by scoring a point--something you wouldn't do with a patient--you reveal acceptance of the fact that I am not Mersey. Your rules would not permit you to give him an unsatisfactory answer."

"Not quite," contradicted Dr. Cloyd, still smiling. "To Mersey, my patient, troubled by his delusion and using all his craft to persuade both of us of its reality, the unsatisfactory answer would be the satisfactory one."

Mersey's voice laughed. "Dr. Cloyd, I salute you. I will leave your world with a tremendous respect for you--and completely unsure of whether you believe in my existence."

"Thank you."

"I am leaving, you know," Mersey's voice replied.

The traveler by now was resigned to letting the patient be his medium and speak his thoughts. Thus far, he had spoken them all truly, if somewhat excessively. The traveler thought he knew why, now, and expected Mersey to voice the reason for him very shortly. He did.

"I'm leaving because I must report failure and advise my people to look elsewhere for a new home. Part of the reason for that failure I haven't yet mentioned:

"Although it might appear that I, the visitor, am manipulating Mersey to speak the thoughts I wished to communicate, the facts are almost the opposite. My control over either Mersey's body or mind is practically nil.

"What you have been hearing and what you hear even now are the thoughts I am thinking--not necessarily the ones I want you to know.

What has happened is this, if I may borrow your theory:

"My mind has invaded Mersey's, but his human vitality is too strong to permit him to be controlled by it. In fact, the reverse is true. His vitality is making use of my mind for its own good, and for the good of your human race. His own mind is damaged badly, but his healthy body has taken over and made use of my mind. It is using my mind to make it speak against its will--to speak the thoughts of an alien without subterfuge, as they actually exist in truth. Thus I am helplessly telling you all about myself and the intentions of my people.

"What is in operation in Mersey is the human body's instinct of self-preservation. It is utilizing my mind to warn you against that very mind. Do you see? That would be the case, too, if a million of us invaded a million minds like Mersey's. None of us could plot successfully against you, if that were our desire--which, of course, it is--because the babbling tongues we inherited along with the bodies would give us away."

The doctor no longer smiled. His expression was grave now.

"I don't know," he said. "Now I am not sure any longer. I'm not certain that I follow you--or whether I want to follow you. I think I'm a bit frightened."

"You needn't be. I'm going. I'll say good-by, in your custom, and thank you for the hospitality and pleasures your world has given me.

And I suppose I must thank Mersey for the warning of doom he's unknowingly given my people, poor man. I hope you can help him."

"I'll try," said Dr. Cloyd, "though I must say you've complicated the diagnosis considerably."

"Good-by. I won't be back, I promise you."

"I believe you," said the doctor. "Good-by."

Mersey slumped back on the couch. He looked up at the ceiling, vacantly.

For a long time there was no sound in the room.

Then the doctor said: "Mersey."

There was no answer. The man continued to lie there motionless, breathing normally, looking at the ceiling.

"Mersey," said the doctor again. "How do you feel?"

The man turned his head. He looked at the doctor with hostility, then went back to his contemplation of the ceiling.

"Drop dead," he muttered.

--RICHARD WILSON