builds up a picture of the outside universe through its
senses. Sometimes its ideas are wrong. Right or wrong, inside everyone's
mind is a universe, derived from the outside universe.

What if the outside universe were derived from something? Derived from
what? The real, logically necessary universe? That could be. At least it
seemed to have some value as a starting point.

He tried to reason from that point. Frustration grew in him. He wished
he were older, had his university education behind him. There were so
many things he couldn't begin to deal with.

Maybe he could take the entire problem to some of his father's friends.
He shook his head over this thought. From all that had gone on it was
too likely that the minute one of them discovered something that would
be of help he would disappear before he could tell it!

That raised another point. Why didn't he himself vanish? What was there
different about him?

A lot. His father had instilled in him a lot of the things he himself
could only aspire to. Unbelief was the major thing. Or perhaps it was
the other major thing, remembrance.

His father's voice came into consciousness, saying something he had said
so many times it was grooved deeply in memory, even to the inflections
of voice. "_All psychoses and mental troubles are caused by walled-off
unpleasant memories. The child who trains himself to recall all
unpleasant things and deliberately associate them with the feeling that
they are valuable lessons, but harmless, will grow up in perfect
balance._"

He smiled. He could let flow through consciousness, dozens of incidents
he had taken up with his father.

He was definitely different than others around him. So different
he had systematically disguised it by a front of accepted
behavior--systematically and consciously, under his father's guidance.

There was a chance those differences made him safe. There was a chance
those differences would make it possible for him to find out what caused
the others to vanish, without he himself vanishing.

The other train of thought inserted itself into consciousness again. Was
belief the key to the disappearances?

* * * * *

Mark Smythe hadn't paid attention when the theory was being explained.
The others had undoubtedly lapped it up. The peculiar thing about the
theory was that it was so logical and so inevitable that the mind tended
to accept it, believe it to be true in spite of the