"Secondly, I can prove to you mathematically that more of them must have escaped from any possible vibrator than have been accounted for. In this connection, I can tell you that if Narodny's method of extermination could have been made efficient I would have wiped them out myself years ago. But I believed then, and it has since been proved, that the survivors of such an attack, while comparatively few in number, would be far more dangerous to humanity than were all their former hordes. "Thirdly, I have here a list of three hundred and seventeen airships; all of which were stolen during the week following the destruction of the automatons' factories. Not one of these ships has as yet been found, in whole or in part. If I am either insane or mistaken, who stole them, and for what purpose?" "Three hundred seventeen--in a week? Why was no attention paid to such a thing? I never heard of it." "Because they were stolen singly and all over the world. Expecting some such move, I looked for these items and tabulated them." "Then--Good Lord! They may be listening to us, right now!" "Don't worry about that," Stone spoke calmly. "This instrument upon my wrist is not a watch, but the generator of a spherical screen through which no robot beam or ray can operate without my knowledge. Certain of its rays also caused your guards to fall asleep." "I believe you," Martin almost groaned. "If only half of what you say is really true I cannot say how sorry I am that you had to force your way in to me, nor how glad I am that you did so. Go ahead--I am listening." Stone talked without interruption for half an hour, concluding: "You understand now why I can no longer play a lone hand. Even though I cannot find them with my limited apparatus I know that they are hiding somewhere, waiting and preparing. They dare not make any overt move while this enormously powerful Fleet is here; nor in the time that it is expected to be gone can they hope to construct works heavy enough to cope with it. "Therefore, they must be so arranging matters that the Fleet shall not return. Since the Fleet is threatened I must accompany it, and you must give me a laboratory aboard the flagship. I know that the vessels are all identical, but I must be aboard the same ship you are, since you alone are to know what I am doing." "But what could they do?" protested Martin. "And, if they should do anything, what could you do about it?" "I don't know," the physicist admitted. Gone now was the calm certainty with which he had been speaking. "That is our weakest point. I have studied that question from every possible viewpoint, and I do not know of anything they can do that promises them success. But you must remember that no human being really understands a robot's mind.