"This is bigger than McCarthy," he said decisively. "We are the only people in this city who suspect a human origin of these phenomena. Other men are yet working, and will continue to work, on the supposition that they are the results of some unbalanced natural conditions. The phenomena are, as yet, harmless. It will not greatly injure the city, once it is prepared, to be without electricity or without sound for limited periods. I doubt very much whether the Unknown can continue these phenomena for longer than limited periods. But conceivably this man may become a peril. He has, if I reason correctly, four arrows in his quiver; the fourth is dangerous. It is our duty to find him before he uses the fourth arrow--if indeed he has discovered the method of doing so. That is always in doubt." Jack's eyes were shining. "Bully!" he cried. "He may conceivably possess the power to launch the fourth and dangerous arrow, but may withhold it unless he believes himself suspected or close pressed. His probable mental processes are obscure. At present he directs himself solely against McCarthy." Percy Darrow had been thinking aloud, and realized it with a smile. "This is one of your jobs, fellow detective," said he. "You've got to be a mark for me to think at." "I wish you'd think a little more clearly," observed Jack. "It sounds interesting, but jumbled. I feel the way I did when I began to read Greek." "McCarthy's incidental," observed Darrow in his detached tone. "Eh?" "Oh, I thought we might as well worry McCarthy by asking him for that job on the side. It's amusing." "What do you want me to do?" asked Jack. "This," said Darrow, with an unusual rapidity of utterance. "See that thick-set, quick man in gray clothes? He's a policeman. In a moment he'll arrest me." "Arrest you--why?" demanded Jack, in tones of great astonishment. "I reason that McCarthy will come to that conclusion. He is beginning to think I have something to do with what he calls his annoyances. I saw it in his eyes. This last curious manifestation came along too pat. You remember, it cut off the dressing-down he was going to give me." Darrow chuckled in appreciation. "Didn't the humor of that strike you?" "Me? Oh, I was scared," admitted Jack. "I want you to go home and tell Helen just what happened in the Atlas Building. Do not tell her that I believe the phenomena are due to any human agency. Say simply that if it is repeated, and she happens to be within the zone of its influence, to keep calm, and wait. It will pass, and it is not to be feared. Tell her I said so." "Lord!" cried Jack. "You don't think it's going to happen again!" "Within the next twenty-four hours," said Darrow. "Oughtn't we to warn the people?" "And let our hidden antagonist know we are aware of his existence?" inquired Darrow. "Anything else?" "No--yes. Buy a gun. If I bring you into any trouble, I'll see you clear. You understand?" "I do." "I rely on your being game."