The telephone bell rang sharply, twice. Professor Augustus S. F. X. Van Dusen — The Thinking Machine — opened his eyes from a sound sleep, rose from the bed, turned on an electric light, and squinted at the clock on the table. It was just halfpast one; he had been asleep for only a little more than an hour. He slid his small feet into a pair of soft slippers and went to the telephone.

“Hello!” he called irritably.

“Is that Professor Van Dusen?” came the answer in a man’s voice — a voice tense with nervous excitement, and so quick in enunciation that the words tumbled over one another.

“Yes,” replied the scientist. “What is it?”

“It’s a matter of life and death!” came the hurried response in the same hasty tone. “Can you come at once and —” The instrument buzzed and sputtered incoherently, and the remainder of the question was lost.

For an instant The Thinking Machine listened intently, seeking to interpret the interruption; then the sputtering ceased and the wire was silent. “Who is this talking?” he demanded.

The answer was almost a shout; it was as if the speaker was strangling, and the words came explosively, with a distinct effort. “My name is —”

And that was all. The voice was swallowed up suddenly in the deafening crack of an explosion of some sort — a pistol shot! Involuntarily The Thinking Machine dodged. The receiver sang shrilly in his ear, and the transmitter vibrated audibly; then the instrument was mute again — the connection was broken.

“Hello, hello!” the scientist called again and again; but there was no answer. He moved the hook up and down several times to attract Central’s attention. But that brought no response. Whatever had happened had at least temporarily rendered his own line lifeless. “Dear me! Dear me!” he grumbled petulantly. “Most extraordinary!”

For a time he stood thoughtfully staring at the instrument; then went over and sat down on the edge of the bed. Sleep was banished now. Here was a problem, and a strange one! Every faculty of his wonderful brain was concentrated upon it. The minutes sped on as he sat there turning it all over in his mind, analyzing it, regarding it from every possible viewpoint, while tiny wrinkles were growing in the enormous brow. Finally he concluded to try the telephone again. Perhaps it had only been momentarily deadened by the shock. He returned to the instrument and picked up the receiver. The rhythmic buzz of the wire told him instantly that the line was working. Central answered promptly.

“Can you tell me the number which was just connected with this?” he inquired. “We were interrupted.”

“I’ll see if I can get it,” was the reply.

“It’s of the utmost importance,” he went on to explain tersely; “a matter of life and death, even.”

“I’ll do what I can,” Central assured him; “but there is no record of the calls, you know, and there may have been fifty in the last ten or fifteen minutes, and of course the operators don’t remember them.” She obligingly gave him a quarter of an hour as she sought some clue to the number.

The Thinking Machine waited patiently for the report, staring dumbly at the transmitter meanwhile, and at last it came. No one remembered the number; there was no record of it. Central was sorry. With a curt word of thanks the scientist called for one of the big newspaper offices and asked for Hutchinson Hatch, reporter.

“Mr. Hatch isn’t in,” came the response.

“Do you know where he is?” queried the scientist, and there was a shadow of anxiety in the perpetually irritated voice.

“No; home, I suppose.”

The man of science drew long, quick breath — it might have been one of uneasiness — and called the newspaper man’s home number. Of course the mysterious message over the telephone had not been from Hatch. It was not the reporter’s voice, he was positive of that, and yet there was the bare chance that —

“Hello!” Hatch growled amiably but sleepily over the wire.

The Thinking Machine’s drawn face showed a vague relief as he recognized the tone. “That you, Mr. Hatch?” he asked.

“Yes.”

“In any trouble?”

“Trouble?” repeated the reporter in evident surprise. “No. Who is this?”

“Van Dusen,” was the response. “Good night.”

Mechanically, unconsciously almost, The Thinking Machine began dressing. The ever active, resourceful brain, plunged so suddenly into this maze of mystery, was fully awake now and was groping through the fog of possibilities and conjecture, feeling for some starting point in this singular problem which had been thrust upon it so strangely. And evidently at last there came some inspiration; for the eminent scientist started hurriedly out the front door into the night, pausing on the steps to remember that in his haste he had forgotten to exchange his slippers for shoes, and that he was bare headed.

Fifteen minutes later the night operator in chief at the branch telephone exchange was favored with a personal call from Professor Augustus S. F. X. Van Dusen. There was a conference of five minutes or so, after which the scientist was led back through the operating room and ushered into a long high ceilinged apartment where thousands of telephone wires were centered — a web woven of thin strands, each of which led ultimately to the long table where a dozen or more girls were on watch. He went into that room at five minutes of two o’clock; he came out at seventeen minutes after four and appeared before the night operator in the outer office.

“I found it,” he announced shortly. “Please, now, let me speak to police headquarters — either Detective Mallory or Detective Cunningham.”

Detective Cunningham answered.

“This is Van Dusen,” the scientist told him. “I should like to know if any murder or attempted murder has been reported to the police tonight?”

“No,” replied the detective. “Why?”

“I was afraid not,” mused The Thinking Machine enigmatically. “Has there been any call for police assistance anywhere?”

“No.”

“Between one and two o’clock?” insisted the scientist.

“There hasn’t been a call tonight,” was the reply. “What’s it all about?”

“I don’t know — yet,” said the scientist. “Good night.”

The Thinking Machine went out after a few minutes, pausing on the curb in the brilliant glare of a street lamp to jot down a number on his cuff. When he looked up a cab was just passing. He hailed it, gave an address to the driver, and a moment later the vehicle went clattering down the street. When it stopped at last before a dark, four-story house, the cabman sat still for a moment expecting his passenger to alight. But nothing happened; so he jumped down and peered into the gloom of the vehicle. Dimly he was able to make out the small figure of the scientist huddled up in a corner of the cab with his huge yellow head thrown back, and slender white fingers pressed tip to tip.

“Here we are, sir,” announced the driver.

“Yes, yes, to be sure!” exclaimed the scientist hurriedly. “I quite forgot. You needn’t wait.”

The vehicle was driven off as The Thinking Machine ascended the brown stone steps of the house and pulled the bell. There was no answer, no sound inside, and he pulled it the second time, then the third. Finally, leaning forward with his ear pressed against the door, he pulled the bell the fourth time. This evidently convinced him that the cord inside was disconnected, and he tried the door. It was locked.

Without an instant’s hesitation he ran down the steps to the basement entrance in an areaway. There was no bell there, and he tried the knob tentatively. It turned, and he stepped into a damp, smelly hallway, unrelieved by one glint of light. He closed the door noiselessly behind him, and stood for a little while listening. Then he did peculiar thing. He produced a small electric pocket lamp, and holding it as far to the left as he could reach, with the lens pointing ahead of him, pressed the button. A single white ray cleft the darkness, revealing a bare, littered floor, moldy walls, a couple of doors, and stairs leading up.

He spent five cautious minutes perhaps in the basement. There was no sign of recent human habitation, nothing but accumulated litter, and dust and dirt. Then he went up the stairs to the floor above. Here he spent another five minutes, with only an occasional flash of light, always at arm’s length to extreme right or left, to tell him there was yet no sign of occupancy. Then another flight of stairs to the second floor. Still there was no sound, no trace of anyone, no indication of a living thing.

His first glimpse of the third floor confirmed at first glance all those impressions of desertion he had gathered below. The front room was identical with the one below, the front hall room was identical; but there was a difference in the large rear room. The dust and litter of the floor seemed worn into a sort of path from the top of the stairs, and following this path toward the back he came upon — a telephone!

“Fortyone-seventeen,” he read, as the instrument stood revealed, bathed in the light from the electric bulb. Then he glanced down at his cuff and repeated, “Fortyone-seventeen.”

With every sense alert for one disturbing sound, he spent two full minutes examining the instrument. He seemed to be seeking some mark upon it — the scar of a bullet, perhaps — and as the scrutiny continued fruitless, the tiny wrinkles, which had momentarily disappeared from his face, appeared there again, and deepened perceptibly. The receiver was on the hook, the transmitter seemed to be in perfect condition, and the walls round the box were smooth. Finally he allowed the light to fade, then picked up the receiver and held it to his ear. His sensitive fingers instantly became aware of tiny particles of dust on the smooth black surface; and the line was dead. Central did not answer. Yet this was the telephone from which he had been called!

Again he examined the instrument under the light, with something akin to perplexity on his drawn face; then allowed his eyes to follow the silken wire as it led up, across the room, and out the window. Did it go up or down? Probably up, possibly down. He had just taken two steps toward that window, with the purpose of answering this question definitely, when he heard a sound somewhere off in the house and stopped.

The light faded, and utter gloom swooped down upon him as he listened. What he heard apparently was the tread of feet at a distance, somewhere below. They seemed to be approaching. Now they were in the lower hall, and grew clatteringly distinct in the emptiness of the house; then the tread sounded on the stairs, the certain, quick step of one who knew his way perfectly. Now the sound was at the door — now finally in the room. Yet there was not one ray of light.

For a little time The Thinking Machine stood motionless, invisible in the enshrouding darkness, until the footsteps seemed almost upon him. Then suddenly his right arm was extended full length from his body, the electric bulb blazed in his hand, and slashed around the room. By every evidence of the sense of sound the flash should have revealed something — perhaps the figure of a man. But there was nothing! The room was vacant, save for himself. And even while the light flared he heard the steps again. The light went out, he took four quick, noiseless steps to his left, and stood there for a moment puzzled.

Then he understood. The mysterious tread was stilled now, as if the person had stopped, and it remained still for several minutes. The Thinking Machine crept silently, cautiously, toward the door and stepped out into the hall. Leaning over the stair rail, he listened. And after awhile the tread sounded again. He drew back into the shadow of a linen closet as the sound grew nearer — stood stockstill staring into blank nothingness as it was almost upon him; then the footsteps receded gradually along the hall, down the stairs, growing fainter, until the receding echo was lost in the silence of the night.

Whereupon The Thinking Machine went boldly up the stairs to the fourth floor, the top. He mounted confidently, as if expecting something to reward his scrutiny; but his eyes rested only upon the bleak desolation of unoccupied apartments. He went straight to the rear room, above the one he had just left, and directly across to one of the windows. Faint, rosy streaks of dawn slashed the east — just enough natural light to show dimly a silken wire hanging down from the middle of the window outside. He opened the window, drew in the wire, and examined it carefully under the electric light, and nodded as if he understood.

Finally he turned abruptly and retraced his steps to the first floor. There he paused to examine the knob of the front door; then went on down into the basement. Instead of examining the door there, however, he turned back under the stairs. There he found another door — a door to the subcellar, standing open a scant few inches. A damp, moldy smell came up. After a moment he pushed the door open slowly and ventured one foot forward in the darkness. It found a step, and he began to descend. The fourth step down creaked suddenly, and he paused to listen intently. Utter silence!

Then on down, ten, eleven, twelve, fourteen, steps, and his foot struck soft, yielding earth. Safely on the ground again, in the protecting gloom, he stood still for a long time, peering blindly around him. At last a blaze of light leaped from the electric bulb, which was extended far from the body to the right, and The Thinking Machine drew a quick breath. It might have been surprise; for within the glow of the light lay the figure of a young man, a boy almost, flat of his back on the muddy earth, with eyes blinking in the glare. His feet were bound tight together with a rope, and his hands were evidently fastened behind him.

“Are you the gentleman who telephoned for me?” inquired The Thinking Machine calmly.

There was no answer, and yet the prostrate man was fully conscious, as proved by the moving eyes and a twitching of his limbs.

“Well?” demanded the scientist impatiently. “Can’t you talk?”

His answer was a flash of flame, the crash of a revolver at short range, and the light dropped, automatically extinguished as the pressure on the button was removed. Upon this came the sound of a body falling. There was a long drawn gasp, and again silence.

“For God’s sake, Cranston!” came the explosive voice of a man after a moment. “You’ve killed him!”

“Well, I’m not in this game to spend the rest of my life in jail,” was the answer, almost a snarl. “I didn’t want to kill anybody; but if I had to, all right. If it hadn’t been for this kid here, we’d have been all right anyway. I’ve got a good mind to give him one too, while I’m at it!”

“Well, why don’t you?” came a third voice. It was taunting, cold, unafraid.

“Oh, shut up!”

Feet moved uncertainly, feelingly, over the soft earth and stumbled upon the inert, limp figure of The Thinking Machine, lying face down on the ground, almost at the feet of the bound man. One of the men who had spoken stooped, and his fingers touched the still, slim body. He withdrew his hands quickly.

“Is he dead?” some one asked.

“My God, man! Why did you do it?” exclaimed the man who had spoken first, and there was a passionate undertone in his voice. “I never dreamed that this thing would lead to — to murder!”

“It hardly seems to be a time to debate why I did it,” was the brutal response; “so much as it is to decide what we’ll do now that it is done. We might drop this body in the coal bin in the basement until we finish up here; but what shall we do with the boy? We are both guilty — he saw it. He wanted to tell the other. What will he do now?”

“He’ll tell it just so surely as he lives,” the bound man answered for himself.

“In that case there’s only one thing to do,” declared Cranston flatly. “We’d better make a double job of this, leave them both here, and get away.”

“Don’t kill me — don’t kill me!” whined the young man suddenly. “I won’t ever tell — I promise! Don’t kill me!”

“Oh, shut up!” snarled Cranston. “We’ll attend to you later. Got a match?”

“Don’t strike a light,” commanded the other man sharply, fearfully. “No, don’t! Why, man, suppose — suppose your shot had struck him in-in the face. God!”

“Well, help me lift it,” asked Cranston shortly.

And between them they carried the childlike body of the eminent man of science through the darkness to the stairs, up the stairs and through the basement to the back. The dawn was growing now, and the pallid, drawn face of The Thinking Machine was dimly visible by a light from the window. The eyes were wide open, glassy; the mouth agape slightly. Overcome by a newborn terror — hideous fear — the two men flung the body brutally into an open coal bin, slammed down the cover, and went stumbling, clattering, out of the room.

It was something less than half an hour later that the lid of the coal bin was raised from inside, and The Thinking Machine clambered out. He paused for a moment, to rub his knees and elbows ruefully and stretch his cramped limbs.

“Dear me! Dear me!” he grumbled to himself. “I really must be more careful.”

And then straight back to the entrance of the subcellar he went. It was lighter outside now, and he walked with the assurance of one who saw where he went, yet noiselessly. But the door of the stairs leading down still revealed only a yawning, black hole. He went on without the slightest hesitation, remembering to step over the fourth step, which had squeaked once before. In the gloom below, standing on the earth again, he listened for many minutes.

Assured at last that he was alone, he groped about the floor for his electric light, and finally found it. Without fear or apparent caution he examined the huge, dark, damp room. On each side were thrown up banks of dirt that seemed to have been dug recently, and here before him was where the bound man had lain. And over there — he started forward eagerly when he saw it — was a telephone! The transmitter box had been wrecked by what seemed to be a bullet. As he saw it he nodded his head comprehendingly.

From there he went on around some masonry. Here was a passage of some sort. He flashed the ligh............