Wednesday night just before retiring he had another disturbing thought. He had explained the theory to his son. But that had been weeks before, and Fred was steeped in the mechanism of unbelief. Good thing, or he might have been the first to disappear.
"What's the matter with you, Martin? Can't you even answer when—" The rest of what his wife was saying faded in the startled realization that he was eating dinner.
"Sorry, dear," he murmured. "I was thinking." He was trying to recall something that might tell him what day it was. It was obviously evening or they wouldn't be eating dinner. "Uh," he said casually, "what day is today?"
"Saturday," Fred said.
"Now Fred, don't tease your father about his absent-mindedness. This is Thursday."
Thursday! That was right. He had given the lecture on the necessity of unbelief today. There was tomorrow, when he could see if any of the class had disappeared yet. He couldn't be certain, of course. Just because a student didn't show up didn't mean he or she had vanished.
He fixed his eyes on Fred, across the table, and smiled. Fred, at least, was a source of comfort. He knew the theory and hadn't vanished.
"Dad," Fred said. "I've been wondering if you saw a point of similarity in the two disappearances?"
Martin thought, good heavens, does he have any inkling of what I've been thinking? Of course not! He's just fumbling. Better to discourage him. "Sorry, son. There aren't any similarities except accidental ones. I've had the confidence of the police on this. The cases are quite unrelated."
Fred refused to be sidetracked. "Dr. Henderson's face lit up as though a sudden idea had struck him. I talked with some of his students. That's what they all thought. And Horace Smith shouted to his wife, 'Ethel! I've got it!' The next instant in each case they vanished into thin air."