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 light into it. it had been dug out of the solid earth, and its existence evidently accounted for the heaps of dirt in the subcellar. still he didn’t hesitate. straight along the passage he went, wary of step, and stooping occasionally to avoid striking his head against the earth above him. ten, fifteen, twenty, feet he went, and still the gloomy, foul smelling hole lay ahead of him, leading to — what? at about thirtyfive feet from the subcellar there was a sharp turn — he thought at first it was the end of the tunnel — then the passage straightened out again, and there was another fifteen or twenty feet, growing smaller and smaller as he went forward.

suddenly the tunnel stopped. the thinking machine found himself flattening his nose against a door of some sort. he allowed his light to fade, then dimly, through a cranny, he saw a faint glow outside. this seemed to be his destination, wherever it was — and he paused thoughtfully. obviously the light outside was electric, and if electric light might not some one be in there? a subterranean chamber of some sort, perhaps? his fingers ran around the edge of the door, loosened a fastening, and he peered out. then, assured again, he opened the door wide, and stepped out into a brilliant glare.

he was in the subway. he stood blinking incredulously. here to his right the shining rails went winding off round a curve in the far distance; and to the left was a quicker turn in the line of the excavation. in neither direction was there anything that looked like a station.

“really, this is most extraordinary!” he exclaimed.

then and there the eminent man of science paused to consider this weird thing from all possible viewpoints. it was unbelievable, positively nightmarish; yet true enough, for here he stood in the subway. there was no question about that; for in the distance was the roar of a train, and he discreetly withdrew into the little door, closing it carefully behind him until it had passed.

finally he popped out again, closed the door behind him, paused only to admire the skill with which a portion of the tiling in the tunnel had been utilized as a door, then went on across the tracks. it was still early morning; the trains were as yet few and far between; so he had a little leisure for the minute examination he made of the tiled walls opposite the closed door. it was perhaps ten minutes before he found a tile that was loose. he hauled at it until it came out in his hand, revealing a dark aperture beyond.

within fifteen minutes, therefore, from the time he undertook the search for the second door he was standing in another narrow, earthy tunnel which beckoned him on. with the ever ready light to guide him, and still proceeding with caution, he advanced for possibly thirty feet; then came a turn. round the turn he found himself in a sort of room — another cellar, perhaps. he permitted his light to go out, and stood listening, straining his squint eyes. after a time he was satisfied and flashed his light again.

directly before him were half a dozen rough steps, leading up to what seemed to be a trap door. he had barely time to notice this and to see that the trap door was hanging open, when there came a cyclonic rush toward him out of the darkness, from the direction of his right, something whizzed past his head, causing him to drop the precious light, and instinctively he ran up the steps. the gloom above was no more dangerous, he thought, than the gloom below, and he went on, finally passing through the trap and standing on a hard floor above.

there was the sound of a fierce, desperate struggle down there somewhere, cursing, blasphemy, then the noise of feet on the steps coming toward him, and the trap door closed with the heavy, resonant clang of iron. he was alone, his light lost. a sudden strange, awful silence closed down around him, a silence alive with suggestion of unseen, unknown dangers. he stood for a moment, then sank down upon the floor wearily.

cashier randall stood beside the ponderous door of the vault, watch in hand. it was two minutes of ten o’clock. at precisely ten the time lock on the massive steel structure, built into the solid masonry of the bank, would bring the mechanism into position for the combination to work. already the various clerks and tellers were at their posts; books and money were in the vault. at length there came a whir and a sharp click in the heavy door, and the cashier whirled the combination. a few minutes later he pulled open the outer door with a perceptible effort, then turned his attention to the combination lock on the second door. this yielded more readily; but there was still another door, the third to be unlocked. altogether the task of opening the huge vault required something like six minutes.

finally cashier randall threw open the light third door, then touched an electric button to his right. instantly the gloom of the structure was dispelled by a flood of light, and he started back in amazement. almost at his feet, on the floor of the vault, was the huddled figure of a man. dead? or unconscious? certainly there was no movement to indicate life, and the cashier stepped backward into the office with blanched face.

others came crowding round and saw, and startled glances were exchanged.

“you, carroll and young, lift him out, please,” requested the cashier quietly. “don’t make any noise about it. take him to my office.”

the order was obeyed in silence. then cashier randall in person went into the vault and ran hurriedly through the piles of money which lay there. he came out at last and spoke to one of the paying tellers.

“the money is all right,” he said, with a relieved expression in his face. “have it all counted carefully, please, and report to me.”

he retired into his private office and closed the door behind him. carroll and young stood staring down curiously at the man who now lay stretched full length on the couch. they looked at the cashier inquiringly.

“i think it’s a matter for the police,” continued the cashier after a moment and he picked up the receiver of the telephone.

“but how — how did he get in the vault?” stammered carroll.

“i don’t know. hello! police headquarters, please.”

“anything missing, sir?” inquired young.

“not so far as we know,” was the reply. “don’t make any excitement about it, please. he is breathing yet, isn’t he?”

“yes,” answered carroll. “he doesn’t seem to be hurt — just unconscious.”

“lack of air,” said the cashier. “he must have been in there all night. it’s enough to kill him. hello! i want to speak to the chief of detectives. mr. mallory, yes. this is the grandison national bank, mr. mallory. can you come down at once, please, and investigate a matter of great importance?”

fifteen minutes later detective mallory walked into the cashier’s private office. instantly his eyes fell upon the recumbent figure on the couch, and there came with the glimpse a strange, startled expression.

“well, for —” he blurted. “where did you get hold of him?”

“i found him in the vault just now when i opened it,” was the reply. “do you know him?”

“know him?” bellowed detective mallory. “know him? why it’s professor van dusen, a distinguished scientist. he’s the fellow they call the thinking machine sometimes.” he paused incredulously. “have you sent for a doctor? well, send for one quick!”

with the tender care of a mother for her child the detective hovered about the couch whereon the thinking machine lay, having first opened the window, and pausing now and then to swear roundly at the physician’s delay in arriving. and at last the doctor came. quick restoratives brought the scientist to consciousness within a few minutes.

“ah, mr. mallory!” he remarked weakly. “please have the doors locked, and put somebody you can trust on guard. don’t let anyone out. i’ll explain in a minute or so.”

the detective rushed out of the room, returning a moment later. he found the thinking machine talking to the cashier.

“have you a man named cranston employed here in the bank?”

“yes,” replied the cashier.

“arrest him, mr. mallory,” directed the thinking machine. “doctor, just the least bit of nitroglycerin, please, in my left arm, here. and, also, mr. mallory, arrest any particular chum of this man cranston; also a young man, almost a boy, possibly employed here — probably a relative or closely connected with cranston’s chum. that will do, doctor. thanks! anything stolen?”

the detective glanced inquiringly at the cashier.

“no,” replied that official.

the thinking machine dropped back on the couch, closed his eyes, and lay silent for a moment.

“pretty bad pulse, doctor,” he remarked at last. “charge your hypodermic again. what bank is this, mr. mallory?”

“grandison national,” the detective informed him. “what happened to you? how did it come you were in the vault?”

“it was awful, mr. mallory — awful, believe me!” was the reply. “i’ll tell you about it after awhile. meanwhile be sure to get cranston and —”

and he fainted.

twenty-four hours’ rest in his own home, under the watchful eye of a physician, restored the thinking machine to a physical condition almost normal. but the whys and wherefors of his mysterious presence in the vault of the bank were still matters of eager speculation, but speculation only, to both the police and the bank officials. his last words, before being removed to his own apartments, had been a warning against the further use of the vault; but no explanation accompanied it.

meanwhile detective mallory and his men rounded up three prisoners — harry cranston, a middle aged and long trusted employee of the bank; david ellis burge, a young mechanical engineer with whom cranston had been upon terms of great intimacy for many months; and richard folsom, a stalwart young nephew of burge’s, himself a student of mechanical engineering. they were held upon charges born in the fertile mind of detective mallory, carefully isolated from one another and from the outside.

the thinking machine told his story in detail, incident by incident, from the moment of the telephone call until the trap door closed behind him and he found himself in the vault of a bank. his listeners, detective mallory, president hall and cashier randall of the grandison national, and hutchinson hatch, reporter, absorbed it in utter amazement.

“certainly it was the most elusive problem that has ever come under my observation,” declared the diminutive man of science. “it was so elusive, so compelling, that i indiscreetly placed my life in danger twice, and i didn’t know definitely what it all meant until i knew i was in the vault. no man may know that slow suffocation, that hideous gasping for breath as minute after minute went by, unless he has felt it. and, gentlemen, if i had been killed one of the most valuable minds in the sciences would have been lost. it would have been nothing less than a catastrophe.” he paused and settled back into that position which was so familiar to at least two of his hearers.

“when i got the telephone call,” he resumed after a moment, “it told me several things beyond the obvious. the logic of it all — and logic, gentlemen, is incontrovertible — was that some man was in danger, in danger even as he talked to me, that he had tried to reach me, seeking help, that the first interruption on the wire came because perhaps he was being choked, and that the second came — the shot which wrecked the instrument — as a desperate expedient to prevent further conversation. the scene was quite clear in my mind.

“the wire was dead then. central didn’t know the number. there was no way to get that number save by the tedious process of testing the wires in the exchange, and that might have taken days. it took only two hours or so, fortunately; but i got the number at last from which i was called; that is, i got a wire which was inexplicably dead, and assumed the rest. the number of that wire was fortyone-seventeen. the records showed the street and number of the house where it came from. therefore i went there. before i went i took the precaution of calling up police headquarters to see if any report of a murder or attempted murder or anything unusual had come in. nothing had come in. this fact in itself was elucidating, because vaguely it indicated that i had been called, rather than the police, because — well, perhaps because it was not desirable for the police to know.

“well, as i explained, i searched the house; and by the way, mr. mallory, i don’t know if you know the advantages of always holding your dark lantern as far away from your body as possible when going into dangerous places; because if there is danger, a shot, say, the natural impulse of the person who shoots is to aim at the light. incidentally this precaution saved my life in the cellar, when i feigned death. but i’m going a little ahead of myself.

“i found telephone number fortyone-seventeen, and there was a heavy coat of dust on the receiver. obviously it had not been recently used. the line was dead, it is true, but the instrument was in perfect condition. there was no sign of a bullet mark anywhere round or near it. if the bullet that was fired had killed the man who had been using the line, it would not have deadened the wire; therefore instantly i saw that the line had been tapped somewhere; that this instrument had been cut off from it, and the instrument which was demolished was the one on the branch wire.

“i knew this, and was going to the window to see if the wire led up or down, when i heard some one approaching. i first supposed that the person, whoever it was, was in the room with me, the steps were so distinct; but when i flashed the light, intending at least to see him, i knew he was above me. one loses the sense of direction of sound, particularly in the dark; and it is an incontestable fact that footsteps, or any sound above, can be heard more clearly than the same sound below. therefore i knew that some one was in the room above me. for what purpose? possibly to disconnect the branch wire on the telephone line.

“i waited until the person, whoever it was, came down and went his way; then i found the wire, and saw where the connection had been made on it. then i went straight down to the subcellar. there i saw this folsom lying on the ground, bound. he was not gagged; yet he didn’t answer my questions; obviously because he knew if he did he would place himself in danger. the shot was fired at me, or rather at my light, and i went through the farce which ultimately placed me in a coal bin. then i began to get a definite idea of things from the conversation, when cranston’s name was mentioned several times.

“folsom persisted in an outspoken declaration to reveal everything he knew, including the story of my murder. he insisted until he placed himself in grave danger, and then, under cover of utter darkness, i extended one hand and pinched him twice on the ankle. he knew then that i was not dead, that i had heard, and did the very thing i wanted him to do — begged for his life. it was a bit of justifiable duplicity. i knew if he was the man his every act so far had indicated that he would humbug cranston and the other man into letting him go, or at least not committing another murder. subsequent developments showed that this conjecture was correct.

“from the coal bin i went back to the subcellar, knowing positively now that there would be no one there. those men were frightened when they left me, and men run from fright. what they would do with young folsom i didn’t know. there, with my electric light, i found the branch telephone. the transmitter box had been ruined by a shot, as i imagined. so, thus far at least, the logic of the affair was taking me some place.

“and then i followed that tunnel through the subway into another tunnel. i should not have ventured into that second tunnel had i not been fairly confident that no one else was there. in that i was mistaken. i don’t know now, but i imagine that young folsom was temporarily being held prisoner there, and that possibly cranston was on guard. anyway, there was a fight, and the trap door was open — the trap door into the vault. and i don’t know yet whether folsom and cranston, if they were there, even knew i was at hand. certainly the trap door, once closed behind me, was not opened again. and you know the rest of it.” again there was a pause, and the scientist twiddled his fingers idly.

“now it all comes down to this,” he concluded at last. “cranston dragged burge in to the affair — burge is a mechanical engineer, and a good one was needed to do this work — they rented the house, and went to work. it took weeks, perhaps months, to do it all. folsom in some way learned of it, and he is an honest man. he took a desperate means of getting the information into my hands, instead of the hands of the police. why the telephone was in the house i don’t know — perhaps it was already there, perhaps they had it put in. anyway, of your prisoners, mr. mallory, this young folsom is guilty only of an attempt to shield his uncle, burge, while cranston is the ringleader, and burge the man who achieved the immense task of getting under the vault of the bank.

“this vault has a floor of cement, cut into small squares. the trap door is in that floor, and so perfectly concealed in the lines of the squares that it is invisible unless submitted to a close scrutiny, just as the doors in the tiled walls of the subway were invisible to a casual observer. they overcame tremendous difficulties, these two men, in cutting through the immense foundation of the vault, even the steel itself, but remember that they worked at night for weeks and weeks, and were making no mistakes. they did not actually rob the bank because, i imagine, they were awaiting the deposit there of some immense sum. is that correct, mr. hall?”

president hall started suddenly. “yes, in a week or so we were expecting a shipment of gold from europe — nearly three million dollars,” he explained. “think of it!”

detective mallory whistled. “phew! what a haul it would have been!”

“now, mr. mallory, either of these three men, if properly approached, will confess the whole thing substantially as i have told it,” remarked the thinking machine. “but i would advise that folsom be allowed to go. he is really a very decent sort of young man.”

when they had all gone except hatch, the eminent man of science went over and laid one hand upon the report’s shoulder and squinted straight into his eyes for a moment. “you know, mr. hatch,” he said, and there was a strange note in the irritable voice, “my first fear, when the telephone call came, was that it was you. you must be careful — very careful, always.”