For his share in the foregoing Percy Darrow was extensively blamed. It was universally conceded that his action in permitting Monsieur X to continue his activities up to the danger point was inexcusable. The public mind should have been reassured long before. Much terror and physical suffering might thus have been avoided--not to speak of financial loss. Scientific men, furthermore, went frantic over his unwarranted destruction of the formulas. Percy Darrow was variously described as a heartless monster and a scientific vandal. To these aspersions he paid no attention whatever.

Helen Warford, however, became vastly indignant and partisan, and in consequence Percy Darrow's course in the matter received from her its full credit for a genuine altruism. Hallowell, also, held persistently to this point, as far as his editors would permit him, until at last, the public mind somewhat calmed, attention was more focused on the means by which the man had reached his conclusions rather than on the use of them he had made.

The story was told three times by its chief actor: once to the newspapers, once to the capitalists from whom he demanded the promised reward, and once to the Warfords. This last account was the more detailed and interesting.

It was of a late afternoon again. The lamps were lighted, and tea was forward. Helen was manipulating the cups, Jack was standing ready to pass them, Mr. and Mrs. Warford sat in the background listening, and Darrow lounged gracefully in front of the fire.

"From the beginning!" Helen was commanding him, "and expect interruptions."

"Well," began Darrow, "it's a little difficult to get started. But let's begin with the phenomena themselves. I've told you before, how, when I was in jail, I worked out their nature and the fact that they must draw their power from some source that could be exhausted or emptied. You have read Eldridge's reasoning as to why he thought Monsieur X was at a distance and on a height. He took as the basis of his reasoning one fact in connection with the wireless messages we were receiving--that they were faint, and therefore presumably far distant or sent by a weak battery. He neglected, or passed over as an important item of tuning, the further fact that the instrument in the Atlas Building was the only instrument to receive Monsieur X's messages.

"Now, that fact might be explained either on the very probable supposition that our receiving instrument happened in what we may call its undertones to be the only one tuned to the sending instrument of Monsieur X; or it might be because our instrument was nearer Monsieur X's instrument than any other. This was unlikely because of the quality of the sound--it sounded to the expert operator as though it came from a distance. Nevertheless, it was a possibility. Taken by itself, it was not nearly so good a possibility as the other. Therefore, Eldridge chose the other.

"There were a number of other strictly scientific considerations of equal importance. I do not hesitate to say that if I had been influenced only by the scientific considerations, I should have followed Eldridge's lead without the slightest hesitation. But as I told him at the time, a man must have imagination and human sympathy to get next to this sort of thing.

"Leaving all science aside, for the moment, what do we find in the messages to McCarthy? First, a command to leave within a specified and brief period; second, a threat in case of disobedience. That threat was always carried out."

Darrow turned to Mrs. Warford.

"With your permission, I should like to smoke," said he. "I can follow my thought better."

"By all means," accorded the lady.

Darrow lighted his cigarette, puffed a moment, and continued:

"For instance, at three o'clock he threatens to send a 'sign' unless McCarthy leaves town by six. McCarthy does not leave town. Promptly at six the 'sign' comes. What do you make of it?"

Nobody stirred.

"Why," resumed Darrow, "how, if Monsieur X was a hundred miles or so away, as Eldridge figured, did he know that McCarthy had not obeyed him? We must suppose, from the probable fact of that knowledge, that either Monsieur X had an accomplice who was keeping him informed, or he must be near enough to get the information himself."

"There is a third possibility," broke in Jack. "Monsieur X might have sent along his 'sign' at six o'clock, anyhow, just for general results."

Darrow nodded his approval.

"Good boy, Jack," said he. "That is just the point I could not be sure about. But finally, at the time, you will remember, when I predicted McCarthy's disappearance, Monsieur X made a definite threat. He said," observed Darrow, consulting one of the bundle of papers he held in his hand:

"'My patience is at an end. Your last warning will be sent you at nine-thirty this morning. If you do not sail on the _Celtic_ at noon, I shall strike,' and so forth. The _Celtic_ sailed at noon, without McCarthy. At twelve thirty came the first message to the people calling on them to deliver up the traitor that is among you.' How did Monsieur X know that McCarthy had not sailed on the _Celtic_? The answer is now unavoidable: either an accomplice must have sent him word to that effect, or he must have determined the fact for himself.

"I eliminated the hypothesis of an accomplice on the arbitrary grounds of plain common sense. They don't grow two such crazy men at once; and one crazy man is naturally too suspicious to hire help. I took it for granted. Had to make a guess somewhere; but, contrary to our legal friends, I believe that enough coincidences indicate a certainty. But if Monsieur X himself saw the _Celtic_ sail without McCarthy, and got back to his instrument within a half-hour, it was evident he could not be quite so far away as Eldridge and the rest of them thought."

"One thing," spoke up Jack, "I often wondered what you whispered to Simmons to induce him to pass those messages over to you. Mind telling?"

"Not a bit. Simmons is an exceptional man. He has nerve and intelligence. I just pointed out to him the possibility that Monsieur X might have control over heat vibrations. He saw the public danger at once, and realized that McCarthy's private rights in those messages had suddenly become very small."

Jack nodded. "Go ahead," said he.

"I had already," proceeded Darrow, "found out where the next wireless station is located. Monsieur X must be nearer the Atlas station than to this other. It was, therefore, easy to draw a comparatively small circle within which he must be located."

"So far, so good," said Helen. "How did you finally come to the conclusion that Monsieur X was in the next office?"

"Do you remembe............