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 assumed 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 passed 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 passed 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 space.
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 passed 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 shells 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.
"There will be a meeting there tonight," came the voice in an impressive tone. "The criminal himself will be present. You can capture him — and with him evidence that will prove his guilt."
"What evidence?"
"Bombs!" the voice was sibilant. "Partly finished bombs! But remember, your enemy is dangerous. Unless you follow my plans exactly, you will not capture him. Do you understand?"
"Yes," replied Cardona.
"Wait in back of the house," came the voice. "Be there after dark with a squad of men. Lie low. Give no sign of your presence. Do you note the window marked with a tiny X?"
"Yes."
"Enter there. Advance to the door of the central room. Go no farther. That is the danger zone. Wait there. The escaping criminal will be forced to choose that exit. And that criminal will be — The Black Master!"