Jack Warford started to say something, but the scientist cut him short.
"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.