When, three hours previous, Darrow had arisen with the remark before chronicled, Jack Warford had followed him in the expectation of a long expedition. To the young man's surprise it lasted just to the hall. There Darrow stopped before the blank door of an apparently unused office. Into the lock of this he cautiously fitted a key, manipulated it for a moment, and turned to Jack with an air of satisfaction.

"You have your gun with you?" he asked.

Jack patted his outside pocket.

"Very well, now listen here: I am going to leave the key in the lock. If you hear me whistle sharply, get in as quickly as you know how, and get to shooting. Shoot to kill. If it happens to be dark and you can not make us out, shoot both. Take no chances. On your quickness and your accuracy may depend the lives of the whole city. Do you understand?"

"I understand," said Jack steadily. "Are you sure you can make yourself heard above all this row?"

Darrow nodded, and slipped inside the door.

He found the office chamber unlighted save by the subdued illumination that came in around the drawn shades of the window. Against the dimness he could just make out the gleaming of batteries in rows. An ordinary deal table supported a wireless sender. A figure stood before the darkened window, the figure of a little, old, bent man facing as though looking out. Through the closed casement the roar of the panic-stricken city sounded like a flood. The old man was in the attitude of one looking out intently. Once he raised both arms, the fists clenched, high above his head.

Darrow stole forward as quietly as he could. When he was about half-way across the room the old man turned and saw him. For the briefest instant he stared at the intruder; then, with remarkable agility, cast himself toward the table on which stood the wireless sender. Darrow, too, sprang forward. They met across the table. Darrow clutched the old man's wrists.

Immediately began a desperate and silent trial of strength. The old man developed an unexpected power. The table lay between them, prohibiting a closer grip. Inch by inch, impelled by the man's iron will, his hand forced his way toward the sending key. Darrow put forth all his strength to prevent. There was no violent struggle, no noise; simply the pressure of opposing forces. Gradually the scientist's youth prevailed against the older man's desperation. The hand creeping toward the sender came to a stop. Then, all at once, the older man's resistance collapsed entirely. Darrow swept his arm back, stepped around the table, and drew his opponent, almost unresisting, back to the window.

"Jack!" he called.

At the sound of his voice the old man gathered his last vitality in a tremendous effort to jerk loose from his captor. Catching Darrow unawares, he almost succeeded in getting free. The flash was too brief. He managed only to rap the young man's head rather sharply against a shade-fitting of the window.

The outer door jerked open, and Jack Warford leaped into the room, revolver in hand. Darrow called an instant warning.

"All right!" he shouted. "Turn on the light, next to you somewhere. Shut the door."

These orders were obeyed. The electric flared. By its light the office was seen to be quite empty save for a cabinet full of books and papers; rows and rows of battery jars; the receiving and sending apparatus of a wireless outfit; the deal table, and one wooden chair. Darrow looked around keenly.

"That's all right, Jack," said he. "Just get around here cautiously and raise the window shade. Look out you don't get near that table. That's it. Now just help me get this man a little away from the table! Good! Now, tie him up. No, bring over the chair. Tie him in that chair. Gently. That's all right. Whew!"

"You're hurt," said Jack.

Darrow touched his forehead.

"A bump," he said briefly. "Well, Jack, my son, we've done it!"

"You don't mean to say--" cried Jack.

Darrow nodded.

"Now, my friend," he addressed the huddled figure in the chair, "the game is up. You are caught, and you must realize it." He surveyed the captive thoughtfully. "Tell me, who are you?" he added. "I should know you, for you are a great discoverer."

The old man stared straight at his interlocutor with his expressionless eyes, behind which no soul, no mind, no vitality even seemed to lie.

Darrow asked him several more questions, to which he received no replies. The man sat like a captured beast.

"I'm sorry," said Darrow to Jack. "I should like to have talked with him. Such a man is worth knowing; he has delved deep."

"He'll talk yet, when he gets over his grouch," Jack surmised.

But Darrow shook hi............