"But there must be some way—"
"Let me finish. There is another factor which you may have failed to consider, one that you could not be expected to know. The men on our ship never once came in direct physical contact with any object on Mars or among the items brought back from that planet. The landing party was never directly exposed even to the Martian atmosphere. It was too great a risk. A protective wall always interposed between the men and the objects they contacted. Nothing was touched by human hands. So how would a parasite have made entry?"
"I don't know!" I said harshly. "But it happened!"
Something stirred in my mind, something urged into activity by Dr. Temple's words, but the moment I concentrated on it, trying to isolate it, a door seemed to close solidly down a dimly lighted corridor of my mind.
"Maybe it was dormant when it was brought in," I said desperately. "Maybe it didn't show up under the tests. How can we be so sure our instruments tell us everything?"
For a moment the scientist did not answer. I saw the compassion in his eyes and knew that he did not believe the aliens existed. He was trying to be kind and patient. I was taking up a great deal of his valuable time but he gave no indication of this. His pipe had burnt out again and now he set it carefully in the big ash tray on his desk. He leaned forward.
"Mr. Cameron, I am a scientist. When I'm presented with a strange new set of facts or apparent facts, even if they seem to contradict my own established theories, I have to consider them. I must try to let the facts speak for themselves without my imposing a preconceived meaning upon them. I've tried not to do that with what you've told me. I've tried to consider seriously the theory or explanation you've offered for the particular set of facts. However, when investigation appears to preclude one possible explanation we have to look for another, an alternative meaning, and see if it will provide a vessel into which the facts might fit precisely. In the present situation there does seem to be another possible answer."
"I know what you're going to say—"
"There may be no alien minds," Dr. Temple said quietly. "Or rather, there may be only one. Your own."
The words dropped with a brutal finality into my brain.