"

While the welcome message was being flashed, MacHeath shut off the
testing instruments and disconnected them. It was possible to
compensate a little for the testing equipment, but a telephone, or
even an electric flashlight, would simply add to the burden.

Bill Griffin shoved down the key on the lamp he was holding and locked
it into place. The shutters remained open, and the lamp shed a beam of
white light along the shining walls of the cylindrical tube. "How much
longer do you figure it'll take, Dave?" he asked.

"Another shift, at least," said MacHeath, picking up the compact,
shielded instrument case. "You want to carry that mat?"

[Illustration]

Griffin picked up the thick sponge-rubber mat that the instrument case
had been sitting on, and the two men started off down the tube,
walking silently on the sponge-rubber-soled shoes which would not
scratch the glass underfoot.

"Any indication yet as to who our saboteur is?" Griffin asked.

"I'm not sure," MacHeath admitted. "I've picked up a couple of leads,
but I don't know if they mean anything or not."

"I wonder if there _is_ a saboteur," Griffin said musingly. "Maybe
it's just a run of bad luck. It could happen, you know. A statistical
run of--"

"You don't believe that, any more than I do," MacHeath said.

"No. But I find it even harder to believe that a materialistic
philosophy like Communism could evolve any workable psionic
discipline."

"So do I," agreed MacHeath.

"But it can't be physical sabotage," Griffin argued. "There's not a
trace of it--anywhere. It _has_ to be psionic."

"Right," said MacHeath, grinning as he saw what was coming next.

"But we've already eliminated that. So?" Griffin nodded firmly as if
in full agreement with himself. "So we follow the dictum of the
Master: 'Eliminate the impossible; whatever is left, no matter how
improbable, is the truth.' And, since there is absolutely nothing
left, there is no truth. At the bottom, the whole thing is merely a
matter of mental delusion."

"Sherlock Holmes would be proud of you, Bill," MacHeath said. "And so
am I."

Griffin looked at MacHeath oddly. "I wish I was a halfway decent
telepath, I'd like to know what's going on in your preconscious."

"You'd have to dig deeper than that, I'm afraid," MacHeath said
ruefully. "As soon as my subconscious has solved the problem, I'll let
you know."

"I've changed my mind," said Griffin cheerfully. "I don't envy your
telepathy. I