the man who'd sold him
the special equipment, and wondered why more criminals didn't know the
equipment existed. It worked; he was sure of that. Fredericks knew
enough of general psi theory to know when somebody was handing him a
snow job. And the equipment was no snow job.

A force shield, that was the basic thing. A shield with no points of
entrance for anything larger than air molecules. Sight and sound could
get through, because the shield was constructed to allow selected
vibrations and frequencies. But no psi force could crack the shield.

Fredericks has sat through a long explanation. Psi wasn't a physical
force; it was more like the application of a mental "set," in the
mathematical sense, to the existing order. But it could be detected by
specially built instruments--and a shield could be set up behind which
no detection was possible. It wasn't accurate to say that a psi force
was blocked by the shield; no construct can block that which has no
real physical existence. It was, more simply, that the shield created
a framework inside of which the universe existed in the absence of
psi.

That wasn't very clear, either, Fredericks thought; but mathematics
was the only adequate language for talking about psi, anyhow. It had
been the theory of sets that had led to the first ideas of structure
and rationality within the field, and the math had gotten
progressively more complex ever since.

Psi couldn't get through the shield, at any rate; that was quite
certain. And very little else could get in, or out. There was only one
point of exit. Unholstering his gun and aiming it automatically keyed
the shield to allow passage of a bullet, and the point of exit was
controlled by the gun's aiming. It was efficient and simple to handle.

But Fredericks wasn't depending on the shield alone. There was a
binder field, too--a field which linked him to the surrounding area,
quite tightly. That took care of the chance that the Psi Operative
would try to pick him up, force shield and all, and throw him out a
window or through the roof. With the binder field in operation, no psi
force could move him an inch.

A plug gas mask, too, inserted into the nostrils. The shield plus the
mask's pack held two hours' worth of air--just in case the Psi
Operative tried to throw poisonous molecules through the force
shield, or deprive him of oxygen.

And then there was the blindfold. Such a simple thing, and so
effective.

* *