THE hand that held the key trembled. At last it found the lock. The key turned. A tall man stepped into the dim hallway, and closed the door behind him.

A slight sigh came from his lips — lips thin and parched, that showed above the heavy muffler which covered the man’s neck, even to his chin.

Slowly, the man moved along the hallway. He turned suspiciously as he reached the stairs, glancing back at the door. The glass transom above it worried him.

He thought of the dark vestibule, which obtained its only rays of light through that very transom. He remembered the nervousness that had gripped him while he had fumbled with the key. He listened, as though he expected some one else to unlock the door.

Now the man laughed nervously. He started up the stairs, his fears banished. His tall, stoop-shouldered figure seemed to stalk upward like a mechanical dummy.

At the landing, halfway to the second floor, he stopped; then continued on his journey, with that same slow, methodical stride.

Another key grated in the lock of the vestibule door. The slight sound began just after the man on the landing had again moved toward the second floor.

The vestibule door opened. A short, broad-shouldered man slipped into the hallway.

He closed the door noiselessly. His eyes gleamed in the dim light as he stared toward the landing below the second floor. His firm face took on a pleased expression.

He followed the course that the first man had taken; but he ascended the stairs with amazing speed and remarkable silence. Two steps at a time he went, one hand on the banister taking part of the burden, he almost vaulted upward. But the strangely gangling figure of the first man was lost in the shadows.

The third floor of the building was darker. When the short, pursuing man arrived there, he stopped at the end of the stairway. His keen ears heard the click of metal. The first man was unlocking a door at the side of the hallway.

Swiftly, the pursuing man advanced through the darkness, keeping against the wall, and moving with his previous stealth. Within a few seconds, he stood only an arm’s length from the tall man at the door. He heard the tall man’s tense, hissing breaths, but the pursuer gave no sign of his own presence.

The door opened inward. The tall man remained motionless in the darkness. He was listening for sounds from downstairs, totally unknowing that a living person stood within a yard of him. Not satisfied, he tiptoed toward the stairway to listen, almost brushing against the hidden man as he went by. After a momentary pause, the tall man returned along the hall. He walked with reassurance. By this time, the short man who had followed him had gone in through the open door.

The tall man closed the door behind him and fumbled for a light switch. A click, and the room was flooded with light. He was in a small, but comfortable, sitting room of a third-story apartment. The tall man seemed confident in the security of his own abode.

He removed his hat, revealing a head covered with black, gray-streaked hair. He drew the muffler from his neck, disclosing the face of a man of fifty. He doffed his coat and placed it on a chair.

There was a mirror at the far side of the room. The tall man stood in front of it and studied his own features. They were well formed except for the chin, which was long and pointed.

The man rubbed his chin reflectively. Then he placed his hands upon his temples to hide the streaks of gray hair. He seemed pleased with his appearance while he held his hands in that position — pleased, despite the worried, haggard expression which dominated his countenance.

OUTSIDE, a driving wind swept around the old house. In the room on the third floor, the windows, one on each side of the mirror, rattled dismally. But that sound did not disturb the man who was engrossed in his own reflection.

He evidently regarded this apartment of the old house on East Eightieth Street as a sanctuary, in which nothing could harm him.

He did not hear the slight click behind him as the wind shook the panes again; he did not see the door open slowly at the other side of the room.

The man studying his reflection lowered his hands from his temples, and a ghostly smile played over his thin lips. They moved, as if muttering words of satisfaction.

A voice spoke behind him.

“Yes, judge,” it said. “A little more black dye is necessary. The gray is showing through. Perhaps it is coming back. That would be unfortunate.”

The man before the mirror stood petrified. He no longer studied his own reflection. His eyes had turned at an angle. They were focused on another figure that also showed in the looking-glass.

He was intently watching the man who had come up behind him, a short, stocky fellow clad in an old coat and soft brown hat. The stranger’s face was not unfriendly, but it bore a look that was both sophisticated and challenging.

The tall man suddenly recovered himself. He swung quickly and faced his visitor. His hands went toward his coat pockets, but stopped on the way. He noticed that the other man’s hands were hidden. Any intention he might have had to draw a gun faded instantly.

“Who are you?” he demanded in a hoarse voice. “How did you come in here?”

“My name is Caulkins,” said the short man, in an affable tone. “I’m the fellow they call the ‘Wise Owl’.”

“The Wise Owl?”

“Yes. With the New York Classic. I’m the chap who gives the low-down on unsolved mysteries. That’s why I’m here tonight.”

“You — you—” The man with the pointed chin began to splutter, but suddenly controlled himself. “Just what,” he asked, with sudden dignity, “is the purpose of your visit? I never knew that newspaper reporters had the privilege of making forcible entry to a man’s home.”

“It wasn’t exactly a forcible entry,” declared Caulkins, with an agreeable smile. “I came in from the hallway when you left the door open.”

THE middle-aged man was studying his visitor closely. He had betrayed signs of nervousness at first; now he felt sure that the speaker was telling the truth.

“Well,” he said quietly, “we’ll forget this intrusion. I might call the police” — he waved his hand toward a telephone — “but I hardly think it’s necessary. If you are really a wise owl, Mr. Caulkins, you will leave here immediately.”

“Not until I have interviewed you,” came the firm reply.

“Interviewed me?” queried the tall man, with feigned surprise. “Why should you interview me? Perhaps you have mistaken me for some one else. My name is Joseph Dodd — Joseph T. Dodd—”

“That’s the name over the bell in the vestibule,” interrupted Caulkins, “but it isn’t your name. You’ve changed your appearance since I last saw you. That was more than a year ago, just before you disappeared — Justice Tolland!”

The older man did not reply. He stared at his visitor, wondering whether to order the reporter to leave or to engage in a discussion with him. Then anger gave way to an expression of cunning on the thin man’s face.

“Why do you think I am Tolland?” the man asked suddenly.

“I know you are!” declared the reporter. “Judge Harvey Tolland disappeared fourteen months ago. Foul play was the story for a while, but I never figured you were dead. Now, why are you here?”

The positiveness in the reporter’s voice was convincing. Had the other man been less anxious, he might have realized that the Wise Owl was bluffing. Caulkins watched him keenly, waiting expectantly for the reply.

It came. The older man pointed to a chair.

“Sit down,” he said, in a hopeless tone. “There’s no use in my trying to deceive you any longer. You are right. I am Judge Harvey Tolland.”

Caulkins dropped into the chair with a broad, triumphant grin. His quest of fourteen months was ended.

The greatest story of the year was in the bag. He had found the missing man, whose strange disappearance had remained unsolved!

He watched intently as the tall judge strode across the room and unlocked a table drawer. Tolland removed a paper from the drawer and thrust it into the reporter’s hands.

“You have asked me a question,” he said grimly. “You want to know why I disappeared. There is the answer!”

Caulkins hastily unfolded the paper. He scanned the written lines that appeared upon it. Suddenly, his hands began to tremble.

The older man, now calm, watched him grimly. The reporter’s eyes were fascinated. They had completed the reading of the message; they were staring at the cryptic signature that appeared beneath it.

Then Caulkins uttered his startled exclamation in words that were gasped through trembling lips.

“A threat from Double Z!”