"I get you!" said the inspector. "All right, professor, we're counting on you!"
Doctor Zerndorff rose and the other men followed. The three went downstairs together in the elevator.
On the ground floor, the professor placed his finger against his lips, and then spoke softly in the mellow light of the empty hallway.
"Up to now," he said, "these men have struck for just one thing — to frighten. Perhaps they shall try to scare again. I think so, yes.
"Perhaps you, Herr Detective, can discover them before they strike! A bomb — you may find somewhere. But after that, they shall not try to scare. They will only protect themselves.
"They may fight, yes? If they do, who is the one they shall fight? The police? I say no! The police are too many.
"Here is the one" — he tapped his chest expressively. "I am the one, yes; the one that they shall fight! They know that I know. You understand? There is danger, or there will be danger, here in New York, for me!"
"That sounds logical, chief," observed Cardona, looking at Inspector Burke.
"So," said Doctor Zerndorff quietly, "do you think that I shall wait? No, no! It is for my own safety that I should see these men in prison.
"You may think of the public, Herr Inspector. That is good. I think, too, of the public — but," he smiled, "I think also of myself!"
He went to the outer door and carefully unbarred it. Standing in semidarkness, he peered across the street. An automobile lurked beside the opposite curb.
"See?" whispered Doctor Zerndorff. "It may be now. I am suspicious. Friend or foe, I know not. So go, my friends, and remember that I shall solve this plot for you!"
Burke and Cardona stepped to the street. The door closed behind them. They heard the click of bolts.
The inspector coughed uneasily.
"Let's get the lay, Joe," he said.
The two men walked boldly across the street. They saw two shadowy forms seated in the front seat of the sedan. Cardona's fingers sought the butt of his automatic.
"What're you doing here, buddies?" he asked.
Something sparkled on the breast of the man beside the wheel. In the reflected light of the street, Cardona recognized the badge of a secret-service agent.
"Hello, Cardona," came a low voice. "That's Inspector Burke with you, eh?"
"Right-o!" replied the detective.
"We watched you go in," came the voice. "We've been waiting for you to come out. We're detailed here to protect Doctor Zerndorff."
Cardona was positive of the identity of the men. He looked at Burke and the inspector nodded his approval.
"We may have a police detail up here, later on," said the detective.
"Okay," came the voice from the car. "Tell them we're here. We'll know them."
Cardona hailed a passing taxi. He waved to the men in the sedan as he and Inspector Burke entered the cab. Then the street became silent. The secret-service men's automobile remained across the street.
The lights in the upstairs apartment went out, but the government men continued their vigil. In their keeping was the safety of the man in whose hands might lie the key to a nationwide plot of which the Manhattan explosions might be but forerunners.
A car going rapidly passed close by the parked automobile. The sharp eyes of the secret-service men were busy as they peered into the darkness of the passing coupe. It contained only the driver. One of the secret-service men sat up suddenly and nudged his companion.
"Did you hear that?" he exclaimed.
"No," said the other, "what was it?"
"It sounded like a low laugh — like a whispered laugh!"
The eyes of the watchers followed the taillight of the coupe until it disappeared in the distance. Then both men settled back to resume their vigil.
One — the man at the wheel — was calm and indifferent. The other was thoughtful and his mind was troubled.
For through his brain passed the haunting recollection of a sinister sound — a laugh so unreal that he could scarcely believe that his ears had not deceived him.
He felt confident that the coupe had come down that street for some special purpose; yet he could not imagine what its mission might have been.
The secret-service man was not acquainted with the underworld of New York. Had he known more, he might have understood. He would have attributed that laugh to more than fancy.
For that tone of sinister merriment had struck terror into the hearts of many gangsters. It was the laugh of The Shadow!
CHAPTER IV. THE HANDS OF THE SHADOW
INSPECTOR BURKE and Detective Cardona were sitting in the office at police headquarters. Outside, through the misty night, a clock boomed out the hour of eleven. The two men had just returned from their interview with Doctor Zerndorff.
Inspector Burke laid a sheet of paper on the desk in front of him. He began to write rapidly in pencil.
Cardona, watching him, knew what he was doing.
Burke possessed a photographic mind. Whenever the inspector held an important interview, he later wrote down the facts from memory. His task completed, Burke handed the sheet of notations to Cardona. The detective read it and nodded in admiration.
"You've got everything there, chief," he said.
Burke smiled and folded the piece of paper. He pocketed it. The next day it would be typed and filed — a record of everything that Doctor Zerndorff had said. This would remain as secret police data.
There was a knock at the door.
"Come in," called Cardona.
A tall, stoop-shouldered man entered. He was clad in overalls. His face was a dull white. He carried a bucket and mop.
Cardona grinned. This was Fritz, the janitor, the faithful servitor of police headquarters.
"Want to clean up, Fritz?" asked the detective.
"Yah," was the reply.
"Well, we're going. You're on the job late again, aren't you?"
"Yah."
Inspector Burke looked at the janitor. He smiled and shook his head.
"I never saw the like of you, Fritz," he observed. "Just because we work late, you work late. I wish some of the force would profit by your example.
"Come on, Joe. We'll let Fritz finish up."
As the men left the room, Fritz was at work. He was dull, slow, and methodical. He continued his task while the footfalls of the departing men echoed from the corridor. Finally he reached the desk where Inspector Burke had been seated.
Here Fritz laid aside his mop, resting it against the wall. From his overalls he drew forth a sheet of thin paper. He studied the surface of the desk and laid the paper upon it. He pressed the sheet flat and rubbed it with his fingers.
His hand was a strange one for a janitor. It was long and supple, and moved with the smoothness of a musician's hand.
Fritz laid the sheet of paper aside. He drew forth a rag and carefully polished the surface of the desk. He put the paper on the desk and finished his mopping.
Then he returned to the paper and carefully rolled it into a tube which he inserted beneath his overalls. He left the room, walked along the corridor to a locker, removed his overalls and put them away. He stowed the mop and bucket in a corner.
He walked with cumbersome step along the corridor until he reached the outside door and stepped out.
A policeman was standing there.
"Good night, Fritz," he called.
"Yah," was the grunted reply.
Fritz shambled around a corner and entered the silence of a narrow alley. Then his form merged with the blackness. Fritz, the janitor, literally had vanished.
A coupe stood a short distance down the alley. Its door seemed to open of its own accord. There was an almost inaudible sound of some garment being swished along the upholstery of the car.
A few moments later, the coupe pulled away. It rolled by police headquarters, then went rapidly uptown, and stopped in another obscure parking place. Here, again, the door seemed to open automatically. Not even the closest observer could have seen a black-clad figure emerging from the interior of the car.