"He is stopping his crimes, then?"

"For the time. But he will begin again, Doctor Zerndorff!"

Gage picked up the newspaper. "You have seen this? An editorial, impeaching Sforza and Pecherkin. It says that their imprisonment has stopped explosions," Gage laughed mirthlessly.

"Stopped explosions! Yes! Until they have been executed! Then The Black Master will begin a new reign of terror!"

"You think so?" There was apprehension in Doctor Zerndorff's tone.

"I know it!" declared Gage emphatically. "Let me tell you of this man, Doctor Zerndorff. "He sought the ruin of Hubert Banks. Four men were in his employ. After they had done his bidding, he destroyed three of them ruthlessly, murdering a score of innocent victims besides. Destroyed them by explosions that seemed designed for terror, yet which were really intended to cover up the murders of individuals! His bomb maker, Vervick, died in an explosion!

"The men he employed to place the bombs are sentenced to death! They are ignorant and blind. They have pictured him as a terrorist, fitting him in as he intended them to do, so that the crimes could be blamed upon Sforza and Pecherkin.

"One man escaped his toils - Perry Warfield. The Black Master employed Killer Bryan to get rid of him.

Also Matthew Stokes.

"I have learned why that man died. He was doing private investigation for Hubert Banks. His work might have led to a discovery of The Black Master.

"It was Killer Bryan who was chosen to do away with Hubert Banks, after the millionaire had been driven insane by financial losses. But that was forestalled, thanks to you, Doctor Zerndorff. So - a new agent was employed - a man wanted by the police. His name was Howard Jennings.

"As valet to Hubert Banks, he worked within the man's home and did The Black Master's bidding, until Banks, virtually insane, killed Jennings and committed suicide.

"There again, we encounter the cunningness of The Black Master. Through his contriving, his own agent perished. Since then, he has worked entirely alone.

"In an effort to protect Hubert Banks, I sent a man named Harry Vincent to counteract the machinations of The Black Master. Vincent was lured to the den of this superfiend. There, in some hideous way, his mind was tortured.

"Vincent suspected danger and sent me a warning before he was captured. I arrived a few hours afterward. I found him in the midst of a deserted house, his mind in a daze.

"What had been a lair of The Black Master was nothing more than an empty building!"

Profound amazement was expressed on Doctor Zerndorff's countenance. His enthusiasm over the convictions of the bombers had been forgotten in the intense interest which had now gripped him.

He studied the face of Clifford Gage. The man showed unmistakable signs of weariness.

"What of this Vincent?" questioned Zerndorff. "He is still stunned, yes?"

"He is improving," replied Gage. "I have placed him in a private sanitarium. He will soon be well; but any reference to his terrible experience would shatter his nerves. He must not be questioned for months to come!"

"And this man you call The Black Master? Have you heard more of him, yes?" Zerndorff continued his questioning.

"I have not! That shows his cleverness. He is working entirely alone. I found one of his tokens beside the body of Howard Jennings. That proved my suspicions regarding the valet. Otherwise I am without a clue."

"He fears you, perhaps?" "No," Gage answered. "He is waiting to begin again after his tools have gone to the electric chair.

"Still, I am working - with a single hope."

"What is that?" Zerndorff asked.

"That he shall make a move to trap me. I, too, am playing a lone hand now. It is because of his craftiness that I may succeed."

"How so?"

"He knows that I will go to any measure to defeat him at the earliest possible moment. I am the attacker.

I must move. He can receive my attack when I am at a great disadvantage. That is one reason why I have come to you." Gage's tone was deeply earnest now.

"To me, yes?"

"To you, Doctor Zerndorff, because at any time, I may meet with unexpected danger that will result in death. Remember all that I have told you, because it will be your fight later on, if I meet with failure now!"

"There is one thing," declared Doctor Zerndorff thoughtfully, "that makes me feel so strongly that this man is active in these bombings. Perhaps it will be a clue, yes. I shall tell you."

There was a definite a.s.surance in the criminologist's tone. Despite Gage's weariness, his eyes sparkled.

"It is about these bombs," continued Doctor Zerndorff. "I have not yet discovered what it is that has made them operate.

"It is not the fuse. It is not the timing. It is not the radio."

"You have constructed duplicate bombs?"

"Yes. But it is of no use. I thought that the radio was the method. I have found the wonderful radio operation for bombs, yes. But it is not the way. Not with the bomb that Vervick has made.

"There is something that is missing! Something which I cannot understand! It must be that there is some sensitive object, of an active agent, like radium, that has discharged those bombs!

"In my search, I have sought many places. I have found that special bits of delicate machinery were bought at certain places. They were ordered sent away.

"The police have investigated, but have learned nothing. They have been satisfied because they have found the extra pieces in the shop of this man Vervick. That has been all they have needed."

The German arose and went to a desk in the corner of the room. He brought out a folded sheet of paper and handed it to Gage.

"Here are the lists that I have made. Perhaps, through these, you may find the clue to The Master. It is probable that he has bought these things and has given them to Vervick. You think so?"

"It is highly probable, doctor!" Gage was enthusiastic. "This may be exactly what I need! After three weeks of hopeless effort, I am anxious to find any clue!"

Doctor Zerndorff bowed. "Let me say one thing," he remarked. "You must be careful. Remember" - he tapped his forehead - "you are to fight against the brain. The man you seek is waiting. I should not like to see you lose your life. I can see the great dangers before you!"

"Dangers. Yes." Clifford Gage smiled wanly. "But there is one danger that I do not fear."

"What is that?"

"Bombings!" Clifford Gage arose and walked to the door. "I won't be blown up - that much is certain.

Not for a while, at least. That work is ended - until these convicted men have been electrocuted.

"After that - well, doctor, I advise you to learn even more than you now know about bombs. You will need to know everything!"

With that, Clifford Gage was gone. The door closed behind him almost before Doctor Zerndorff realized it. The criminologist went to the window. He turned out the lamp beside him and stood staring into the street.

No one appeared there. A long, black shadow flitted beneath the glare of an electric light. Doctor Zerndorff's keen eyes sought to find a form beside it. But no one was visible.

Silently, mysteriously, Clifford Gage had vanished into the night. Once again he had a.s.sumed the unknown personality of the strange being called The Shadow.

Doctor Zerndorff remained beside the upstairs window. Staring and motionless, he waited while long minutes went by, until, at last, he heard a knock at the door of his room.

Otto entered.

"You have not seen anyone downstairs?" questioned Doctor Zerndorff.

"No, Herr Doktor," replied Otto.

Doctor Zerndorff shook his head.

"It is wonderful, yes," he muttered. "They call him The Shadow. He is the man that seems like he is of the night. He brings me the amazement!"

CHAPTER XVIII. MYSTERY HOUSE.

IN uptown Manhattan stood an old, deserted house. Thick bars and gratings protected its windows, even up to the third floor.

The house had become desolate, specterlike, even before the owner's death, a few years before.

Pedestrians shuddered and increased their pace as they pa.s.sed the sinister mansion on dark nights.

No one would openly declare the place was haunted, yet the few who had rented it found some excuse to break their lease.

The new owners shrugged and left the place as it was, hoping that some strange eccentric character, like the former owner, might rent the place.

One tenant at last rented it, at a ridiculously low figure. He made all arrangements by phone and letter, apparently not caring to show himself. The owners did not ask him why he chose to live in such a gloomy place. He had paid the year's rent in advance; that was all they wanted.

Since he moved in with his furniture, no one had seen him either enter or leave the house.

A few months after the new tenant had moved in, a tall, dignified man called at the office of the company which had taken furniture into the weird house. At the man's request the movers told him the exact date of moving the furniture, and also the address from which they had taken the furniture.

That night, the same man might have been seen near the house. He wore dark clothing, and when he walked down the street he seemed to melt into the blackness of the houses across the way.

This continued for two nights. So silently and invisibly was the man's mission accomplished that not even the watchman in a nearby factory noticed the vigil that was being kept.

On the third night, an automobile pa.s.sed along the street before the house. The red reflection of its taillight revealed a momentary shadow on the paved street. That was the only indication of a person's presence.

Shortly afterward, there was a definite motion beside the darkened wall near the rear of the mysterious house. A vague shape rose from the blackness.

Invisible hands engaged the fastenings of the bars on a ground-floor window. Someone was working, cautiously striving to remove the fastening that seemed as permanent as the wall itself.

Many minutes elapsed; there was no sound other than a swishing noise that was almost inaudible. Then the entire grating came away. After that, the window opened noiselessly. A human form glided through the s.p.a.ce.

The glare of a flashlight appeared within the dark house. The light could not be seen outside, for it was focused on the floor and its luminous circle was very small. The light moved through the hallway as though floating in the air.

Not a sound followed it. At last it rested upon a door that was fitted with a lock.

A hand holding a ring of keys came into the circle of light, the lock clicked, and the door opened outward. The light came on. At first it was a tiny circle on the floor. Then came the powerful beam of a larger light that revealed the full interior of the apartment.

The room was draped with pleated black curtains. It was carpeted with a dark covering.

It was the exact counterpart of that room where Howard Jennings had received his last instructions, and in which Harry Vincent had lost his reason!

It was the lair of The Black Master!

The light turned about the room. In its glare appeared the shadow of the man who held it - a long shadow that came and went like a specter of the night. Then the light was turned off. The smaller flash took its place.

The man with the light pa.s.sed through an almost invisible opening in the curtain and cautiously entered a smaller room, with drawn shades and shuttered windows. Here was a curtained niche. The investigator spread the curtains and discovered a broad, old-fashioned windowsill. It was an ideal spot where a man could hide. The light moved across the room. It centered on a desk upon which lay a pile of papers. One by one the prying hand investigated them. It found nothing of importance.

Then it came to a calendar. One date was conspicuous. That was the thirtieth of June. Around it was a small penciled ring. It must signify an appointment.

June the thirtieth was tomorrow!

The man with the light continued his mysterious investigation. He confined his efforts to the first floor.

There was a stairway to the second; also one to the cellar. Both were protected by heavy, double-locked doors.

The man who had made the search continued no further. He was satisfied after he had discovered a locked closet and had opened it. The closet contained an array of firearms on one shelf. Beneath the shelf, at the bottom of the closet, were hollow sh.e.l.ls and bits of mechanism. They were the appliances of a bomb maker. The invisible man laughed softly, in the darkness.

He closed the door and carefully relocked it. The light moved back toward the rear of the house. It disappeared. A form slipped through the window. The sash was lowered noiselessly. The barred grating was replaced and fastened in the darkness.

The next day Detective Joe Cardona received a carefully drawn diagram, showing every detail of the ground floor of the old house with the barred windows.

Cardona was sitting at his desk in headquarters when he received the communication. While he was still puzzling over it, the telephone rang. He answered and listened intently as a low, strangely familiar voice came over the wire.

"You have received a diagram," came the voice. "It is there before you now."

"Yes," replied Cardona in amazement.

"Now I must have your word that you will follow the directions that I give you."

"Go on," interposed Cardona. "I promise!"

"The diagram shows the ground-floor plan of the quarters of the man behind the bomb outrages," the voice continued.

Cardona was too startled to reply.

"The large central room is the danger spot," added the voice. "That is where he lures his victims.

"The place is a trap. The walls are covered with jet-black curtains. The room is wired with electric current.