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 don't envy a guy who has to TP his own subconscious to find out what he's thinking." MacHeath chuckled softly as he turned the bolt that opened the door in the "gun" end of the stripped-nuclei accelerator. The seals broke with a soft hiss. Evidently, the barometric pressure outside the two-mile-long underground tube had changed slightly during the time they had been down there. "It'll be a week before we can test it," MacHeath said in a tired voice. "Even after we get it partly in balance. It'll take that long to evacuate the tube and sweep it clean." * * * * * It was the first sentence he had spoken in the past hour or so, and it was purely for the edification of the man who was standing on the other side of the air lock, although neither Griffin nor MacHeath had actually seen him as yet.