deep silence, then a long shuddering wail of terror, a stifled, strangling cry for help, the sound of a body falling, and again deep silence. a pause, and after awhile the tramp, tramp of heavy shoes through a lower hall. a door slammed and a man staggered out into a deserted street, haggard, trembling and with lips hard set. he reeled down the street and turned the first corner, waving his trembling hands fantastically.

another pause, and spears of light flashed through the black night from the second floor of a great six-story tenement in south boston, then came the sound of stockinged feet hurrying along the hall. half a dozen horror-stricken men and women gathered at the door of the room whence had come the cry, helplessly gazing into one another’s eyes, waiting, waiting, listening.

finally, from inside the room, they heard a faint whispering sound as of wind rustling through dead leaves, or the silken swish of skirts, or the gasp of a dying man. they listened with strained attention until the noise stopped.

at last one of the men rapped on the door lightly. there was no answer, no sound. again he rapped, this time louder; then he beat his fists on the door and called out. still a silence that was terrifying. mute inquiry lay in the eyes of all.

“break in the door,” said some one at length, in an awed whisper.

“send for the police,” said another.

the police came. they smashed in the door, old and rotting from age, and two of them entered the dark room. one of them used his lantern and those who crowded the door heard an exclamation.

“he’s dead!”

peering curiously around the corner of the door the white-faced watchers in the hall saw a man, dressed for bed, lying still on the floor. two chairs had been overturned; the bed clothing was disarranged. one of the policemen was bending over the body, making a hurried examination. he finally arose.

“strangled to death with a rope — but no rope here,” he explained to the other. “this is a case for a medical examiner and detectives.”

“what’s his name?” asked one of the policemen of a man who stood looking in curiously.

“fred boyd,” was the reply.

“have a roommate?”

“no.”

the other policeman was fumbling about the table with his light. at last he turned and held up something in his hand.

“look here,” he said.

it was a new wedding ring. the bright gold glittered in the lantern light.

an hour later a man turned from a side street into the avenue where stood the big tenement house, and swung along in that direction. it was the man who had left the lower door soon after the cries were heard on the second floor. then his face had been haggard, distorted; now it was calm. one might even trace a line of melancholy and regret there.

around the street door of the tenement was gathered a crowd of half a hundred curious ones, half-clad and shivering in the chill of the night, all craning their necks to see into the hall over the broad shoulders of a policeman who barred the door.

from a score of windows the heads of other curious ones were thrust out; there was the hum of subdued conversation.

the stranger paused on the outskirts of the little knot and peered curiously into the hall, as others were doing. he saw nothing, and turned to a bystander.

“what is it?” he asked.

“man murdered inside,” was the short response.

“murdered?” exclaimed the stranger, “who was it?”

“fellow named fred boyd.”

a flash of horror passed over the stranger’s face and he made an involuntary motion with his hand toward his heart. then he steadied himself with an effort.

“how was he — he murdered?” he asked.

“choked to death,” said the other. “somebody heard him yell for help a little while ago, and when a policeman came he smashed in the door and found him dead. the body was still warm.”

the stranger’s face was white as death now and his lips moved nervously. his hands, thrust deep into his pockets, were clenched until the nails cut the flesh.

“what time did it happen?” he said.

“the cop says about fifteen minutes to eleven,” was the reply. “one of the tenants who lived on the second floor, where boyd had a room, looked at his clock when he got up after he heard boyd shout, so they know just when it was.”

uncontrollable terror glittered in the stranger’s eyes, but none noted it. all were intently looking into the hall waiting for something.

“medical examiner barry and detective mallory are up there now,” volunteered the bystander. “the body will be coming out in a minute.”

then an awed whisper went around: “it’s coming.”

the stranger stood peering on as the others did.

“do they know who did it?” he asked. his voice was tense, and he fiercely repressed a quaver in it.

“no,” said his informant. “i heard, though, that a fellow had been up in boyd’s room tonight, and the man who had the next room heard them talking very loud. they had been playing cards.”

“did the man go out?” asked the stranger.

“nobody saw him if he did,” was the reply. “i guess, though, the police know who he was, and they’re probably looking for him by this time. if they don’t know, mallory’ll find him out all right.”

“great god!” exclaimed the stranger between his tightly compressed lips.

the other man turned and looked at him curiously.

“what’s the matter?” he asked.

“nothing, nothing,” said the stranger, hurriedly. “look, there it comes — that’s all. it’s awful, awful, awful.”

the big policeman in the door stepped to one side, and men came out bearing a litter, on which lay a grim, grisly something that had been a man. it was covered with a sheet. beside it were detective mallory and medical examiner barry. the little knot of onlookers was silent in the presence of death.

the stranger looked, looked as if fascinated by the horrid thing which lay there, watched them put the litter into the police ambulance, heard the medical examiner give some instructions and then detective mallory reentered the house. the wagon drove away.

turning suddenly, the stranger strode quickly down the avenue to the first corner. there he turned away and was swallowed up in the darkness. after a moment, from a distance, came the sound of a man’s footsteps, running.

2

several newspaper men, among them hutchinson hatch, went over the scene of the crime with detective mallory. it was a square, corner room on the second floor. the furniture consisted only of a bed, a table, a wash stand, chairs, there was no carpet to cover the gaping cracks in the floor, no curtains on the two windows.

the building was old and poorly constructed. here a part of the cornice was sagging and broken, there the walls were mouldy; the ceiling was blotched with smoke, over by the steam radiator rats had gnawed a hole big enough to put one’s fist in, the single-stemmed gas jet was grimy with dirt.

of the two windows one was in the back wall and one in the side. hutchinson hatch trailed around the room with detective mallory. he saw that the two windows were securely fastened down with a sliding catch over the middle of the lower sash; there were no broken panes so that one leaving by the window might have reached in and fastened it after him.

mr. mallory explored the closet, but found only the things that belong to a poor man: clothing, an old hat, a battered trunk. there was no opening, the walls were solid. then mr. mallory went to the door that had been smashed in. it was the only door except that of the closet.

there was no transom.

mr. mallory and the reporter looked at this door a long time. it had been fastened when the police came — barred with an iron rod from one side to the other — held in round, iron sockets, set in the door facing. neither of the sockets was open at the top; the bar had to be pushed through one straight on across the door into the other.

thus early in the investigation hutchinson hatch saw this problem. if the windows were fastened inside and the murderer could not have passed out that way; if the door was fastened inside with an iron bar in both sockets and the murderer could not have gone that way — what then?

hatch thought instinctively of a certain scientist and logician of note. professor augustus s.

f. x. van dusen, ph. d., m. d., ll. d., etc., so-called the thinking machine, whom he had occasion to know well because of certain previous adventures in which the scientist had accomplished seemingly impossible things.

“and i think this would stump even him,” hatch said to himself with a grim smile.

then he listened as detective mallory questioned the various tenants of the house. briefly the detective brought out these facts:

a man, whose description the detective carefully noted, had called to see boyd that evening about half past eight o’clock. he had been there many times before. four persons had seen him this evening in boyd’s room, but no one of these knew his name. some one passing had seen boyd playing cards with him.

shortly after 10 o’clock, when practically every one in the house had gone to bed, a man and woman in the next room heard boyd’s voice and that of his caller raised suddenly as if in argument. this continued for five minutes or so, then it quieted down. such things were common in the tenement and the man and woman dropped off to sleep, thinking nothing of it.

some time later, evidently only a few minutes, they were awakened by that pitiful, terror-stricken cry which made them shudder. with others in the house who had been aroused they dressed hurriedly. it was then they heard heavy foot steps in the hall below and the street door opened with a bang.

both were of the opinion not five minutes could not have elapsed from the time they heard the cry until they stood outside the door where the man lay. they would have heard, they thought, anyone leave boyd’s room after they were awakened by the cry, yet there was no sound from there when they stood in the hall. then they heard — what?

“it was a peculiar sound,” the man explained. “it struck me first that it was the swish of silk skirt, then, of course, as no woman was in the room, it must have been the dying man breathing.”

“silk skirt! woman! woman! wedding ring!” hatch thought. whose was it? how could a woman have escaped from the room when it seemed that it would have been impossible for a man to escape? the questionings concluded, detective mallory turned graciously to the representatives of the press who were waiting impatiently. it was after midnight, dangerously near the first edition time, and the reporters were anxious for the detective’s comment.

he was about to begin when another reporter, one of hatch’s fellow workers, entered, called hatch to one side and said something quickly. hatch nodded his head and idly fingered a pack of playing cards he had taken from the table.

“good,” he said, “go back to the office and write the story. i’ll ‘phone mallory’s statement and tell him that other thing. i want to do a little more work, but i’ll be at the office by halfpast 2 o’clock.”

the reporter went out hurriedly.

“i suppose you boys want to know something about how all this happened?” the detective was saying. he lighted a cigar and spread his feet wide apart. “i’ll tell you all i can — not all i know, mind you, because that wouldn’t be wise, but how the murder happened, and you can put in the thrill and all that to suit yourself.

“about halfpast 8 o’clock tonight a man called here to see boyd. he knew boyd very well — was probably a friend of several years’ standing — and had called here frequently. we have an accurate description of him. he was seen by several persons who knew him by sight, therefore will be able to absolutely identify him when we arrest him.

“now, those two men were together in this room for possibly two hours. they were playing cards. more than half the murders on record are committed in the heat of passion. these men quarrelled over their game, probably ‘pitch’ or ‘casino’—”

“it’s a pinochle pack,” said hatch.

“then the crime was committed,” the detective went on, not heeding the interruption, “the unknown man was sitting here,” and mallory indicated an overturned chair to his right.

“he leaped like this,” and the detective, with a full eye for dramatic effect, illustrated, “seized boyd by the throat, there was a struggle, notice the other overturned chair — and the unknown man bore boyd down gripping his throat. he choked him to death.”

“i thought the dead man was undressed when he was found?” asked hatch. “the bed, too,” and he indicated its disordered condition.

“he was, but — but it must have happened as i said,” said the detective. he didn’t like reporters who asked embarrassing questions. “his victim dead, the murderer went out by that door,” and he pointed dramatically.

“through the keyhole, i suppose?” said hatch, quietly. “that door was fastened inside as no mere mortal could fasten it after he left the room.”

“it’s an old burglar’s trick to fasten a door after you leave the room,” said the detective, loftily.

“how about the wedding ring?”

“ah!” and the detective looked wise. “there’s nothing to be said of that now.” he saw suddenly that he had made one mistake and he felt his prestige slipping away. the reporters turned a flood of questions upon him: “how did it happen boyd was undressed?”

“who put out the gas?”

“how would a burglar replace an iron bar like that?”

“do you suspect a burglar?”

mr. mallory raised his hand. “i will say absolutely nothing else about the case.”

“let’s see if we understand you,” said hatch, and there was a mocking smile on his lips. “the police theory briefly is this: a man came here, there was a quarrel, a struggle; boyd was killed, choked; then the murderer left this room by that door, possibly through the keyhole or a convenient crack. then, being dead, boyd got up, took off his clothes, turned out the gas, lay down on the floor, screamed for help and died again. is that right?”

“bah!” thundered mr. mallory, on the verge of apoplexy. “perhaps,” he added scornfully, “you know more about it than i do.”

“well, yes, i’ll confess that,” said hatch. “i know at least the name of the man who was here tonight, and these other reporters will know it when their outside men come in.”

“you do, eh,” demanded mr. mallory. “who is it?”

“his name is frank cunningham, a watchmaker of no. 213 — street.”

“then he is boyd’s murderer,” mr. mallory declared. “we’ll have him under arrest in an hour.”

“he has disappeared,” said hatch, and he left the room.

3

from the south boston tenement house hutchinson hatch went to the undertaking establishment where the body of fred boyd lay, made a careful examination of the mark which showed that he had been throttled, and then went in a cab to the home of professor van dusen, the thinking machine. as he drove up he noticed a bright light in the professor’s laboratory. it was just fifteen minutes past 1 o’clock when he ascended the steps.

the thinking machine in person answered the door bell, the leonine head with its shock of yellow hair, the clean shaven face, and the perpetually squinted eyes behind thick glasses standing out boldly and grotesquely in the light from a nearby arc.

“who is it?” asked the thinking machine.

“hutchinson hatch,” said the reporter. “i saw your light and i was particularly anxious for a little advise, so i thought —”

“come in,” said the scientist, and he extended his long, slender fingers cordially.

hatch followed the thin, bowed figure of the scientist, which seemed that of a child, into the laboratory where he was motioned to a seat. then hatch told the story of the crime, so far as it was known, while the professor sat squinting steadily at him, his long taper fingers pressed together.

“did you see the man?” asked the thinking machine.

“yes.”

“what kind of marks, exactly, were those on his neck?”

“they seemed to be such marks as would be made by a large rope drawn about the throat.”

“was the skin broken?”

“no, but whoever strangled him must have had tremendous strength,” said the reporter. “the pressure seemed to have been all around.”

the thinking machine sat silent for several minutes.

“door fastened inside with iron bar,” he mused, “and no transom, so the bar was not placed back in position. both windows fastened inside.”

“it would have been absolutely impossible for any person to leave that room after boyd was dead,” said the reporter, emphatically.

“nothing is impossible, mr. hatch,” said the thinking machine, testily. “i thought i had demonstrated that clearly, once. the worst anything can be is extremely difficult — not impossible.”

hatch bowed gravely. he had walked over one of the thinking machine’s pet hobbies.

“man was undressed,” went on the thinking machine. “bed disordered, chairs overturned, gas out.” he paused a moment, then asked: “you reason that the man must have gone to bed after putting out the light, and that his murderer came upon him unawares?”

“that seems to be the only possible thing to imagine,” said hatch.

“and in that case the other man — cunningham — would not have been there?”

“precisely.”

“what sort of a wedding ring was it?”

“perfectly new. it didn’t seem to have ever been worn.”

the thinking machine arose from his seat and took down a heavy volume, one of hundreds which lined his walls.

“you don’t believe it probable that cunningham left the room while angry and returned after boyd was asleep and killed him?” asked the thinking machine as he fingered the leaves.

“he couldn’t have come back if that door was fastened,” said hatch, doggedly.

“he could have, of course,” said the thinking machine, “but it is hardly probable. do you think it reasonable to suppose then that someone hidden in the closet waited until cunningham was gone and then killed boyd?”

“that sounds more plausible,” said hatch, after a moment’s consideration. “but he couldn’t have gone out of that room and fastened the door or window behind him.”

“of course he could have,” said the thinking machine, irritably. “don’t keep saying he couldn’t have done anything. it annoys me exceedingly.”

properly rebuked hatch sat silent while the thinking machine sought something in the book.

“in the event, of course, that somebody was hidden in the room it would make it a premeditated murder, wouldn’t it?” asked the scientist.

“yes, unquestionably,” replied the reporter.

“here is something,” said the thinking machine, as he squinted into the volume he held. “it is logic reduced to figures. criminologists agree, practically, that thirty and one-third per cent of all premeditated crimes are committed because of money, directly or indirectly; that two per cent are committed because of insanity; and that the others, sixty-seven and two-thirds per cent, are committed because of women.”

hatch nodded.

“we’ll shut out for the time being the matter of insanity — it is only a remote chance; money would hardly enter into the case because of the fact that both men were poor. therefore, there remains a woman. the wedding ring found in the room also indicates a woman, though in what connection is not clear.

“now, mr. hatch,” he continued, glaring at the reporter almost fiercely, “find out all you can about the private life of this man boyd — it will probably be like every other man of his class — and particularly his love affairs; find out also all you can about cunningham and his love affairs. if the name of any woman appears in the case at all, find out all about her — and her love affairs. you understand?”

“yes,” was the reply.

“don’t delude yourself with the thought that it was impossible for anyone to leave that room after boyd was dead,” went on the scientist, with the stubborn persistence of a child. “suppose this — i don’t offer it as a solution — suppose that boyd had been engaged to be married, that someone else loved the girl he was to marry, that that someone else had hidden in his room until cunningham went away, then — you see?”

“by george!” exclaimed the reporter. “i never thought of that. but how did he get out?” he added helplessly.

“if a man did do such a thing he would have made every arrangement to leave that room in a manner calculated to puzzle anyone who came after. mind, i don’t say this is what happened at all — i merely suggest it as a possibility until i find more to work on.”

hatch arose, stretched his long legs and thanked the thinking machine as he pulled on his gloves.

“i’m sorry i could not have been of any more direct assistance,” said the scientist. “when you do these things i ask come back to see me — i may be able to help you then. you see i’m at a tremendous disadvantage in not having seen the place where boyd was killed. there is one thing, though, which i particularly would like for you to find out for me now — tonight.”

“what is it?” asked hatch.

“this tenement is an old building, i understand. i should like to know if the occupants have ever been annoyed by rats and mice, and if they are so annoyed now?”

“i don’t quite see —” began the reporter in surprise.

“of course not,” said the thinking machine petulantly. “but i should like to know just the same.”

“i’ll find out for you.”

hutchinson hatch had still nearly an hour, and he drove to the tenement in south boston, to wake up its occupants and ask them — of all the silly questions in the world —“are you annoyed by mice?” he set his teeth grimly and smiled.

when he reached the tenement he went straight on to the second floor. the steps ended within a few feet of the door where the crime had been committed. hatch looked at the door curiously; the police had gone, the room was silent again, hiding its own mystery.

as he stood there he heard something which startled him. it came from the room where boyd had been found dead. there was no question of that. it was a faint whispering sound as of wind rustling through dead leaves, or the silken swish of skirts, or the gasp of a dying man.

with blood tingling, hatch rushed to the door and threw it open. he stepped inside, lighting a match as he did so. the room was empty save for the poor furniture. no sign of as living thing!

4

straining his ears to catch every sound, hatch stood still, peering this way and that until the match burned his fingers. then he lighted another and still another, but there was no repetition of the noise. at last the ghostly quiet of the room, its gloom and thoughts of the mystery which its walls had witnessed began to press on his nerves. he laughed shortly.

“a very pronounced case of enlargement of the imagination,” he said to himself, and he passed out. “this thing is getting on my nerves.”

then, feeling very foolish, he aroused several persons and inquired solicitously as to whether or not they had ever been troubled with mice or rats, and when this annoyance had stopped, if it had stopped.

the concensus of opinion was that it was a silly thing to ask, but that up to a fortnight ago the rodents had been very bad. since then no one had noticed particularly. these things, in so far as they related to rodents of any kind, were telephoned to the thinking machine.

“uh, huh,” he said over the ‘phone. “thanks. good night.”

from that point on every effort of the police and the press was directed to finding frank cunningham, who was openly charged with the murder of fred boyd. his disappearance had been complete. if there had been any doubt whatsoever of his guilt, this was convincing — to the police.

it was hatch’s personal efforts that uncovered the fact that cunningham had had a bank account of $287 in a small institution, that on the morning following the mysterious crime in the south boston tenement a check to “cash” had been presented for the full sum and that check had been honored. this began to look conclusive.

it was also due to hatch’s personal efforts that the police learned cunningham was to have been married a week after his disappearance to caroline pierce, a working girl of the west end. then hatch discovered that caroline pierce had also disappeared; that she went away presumably to work on the morning after the murder of boyd. where had she gone? no one knew, not even miss jerrod, the girl who, with her, occupied a suite of three rooms in the west end. why had she gone? no one knew that. when had she gone? still no one knew. when would she return? again the same answer.

to the reporter there seemed only one plausible explanation. this was that cunningham had drawn his money from the bank — which he had saved to make a little home for the girl he loved — and they had gone away together. in the natural course of his duty hatch printed this, and it came to the eyes of the police. detective mallory smiled.

but the wedding ring in boyd’s room?

there was no explanation of that. boyd had had no love affair so far as any one knew. he had been a hard-working, steady-going man in his trade — electrician employed by a telephone company — and he and cunningham had been friends since boyhood.

all these things, while interesting in themselves, still threw no light on the actual crime. who killed boyd, and why? how did the murderer get away? hatch had put the question to himself time and again. there was no answer. thus the intangible pall of mystery which lay over the happenings in the south boston tenement was still impenetrable.

on the second day after the crime hatch again consulted the thinking machine. the scientist listened patiently and carefully, but without any enthusiastic interest to the reporter’s recital of what he had discovered.

“have you a man watching the place where the girl lives?” he asked.

“no,” hatch replied. “i think she’s gone for good.”

“i don’t think so,” said the thinking machine. “i should send a man there to see if she returns.”

“if you think best,” said hatch. “but don’t you think now this man cunningham must have been the criminal?”

the scientist squinted at the reporter a long time, seemingly having heard nothing of the question.

“it looks that way to me,” hatch went on, hesitatingly. “but frankly, i can’t imagine a way that he might have left that room after boyd was dead.”

still the scientist was silent, and the reporter nervously fingered his hat.

“that information you gave me about the rats was very interesting,” said the thinking machine at last, irrelevantly.

“perhaps, but i don’t see how it applies.”

“looking out the windows of the room where boyd was found, what did you see?” the scientist interrupted.

hatch did not recall that he had ever looked out either of the windows; he had merely satisfied himself that neither had been used as a means of exit. now he blushed guiltily.

“i’m afraid you haven’t looked,” said the thinking machine, testily. “i thought probably you wouldn’t have. suppose we go to south boston this afternoon and see that room.”

“if you only would,” said hatch, delightedly. here was better luck than he dreamed of. “if you only would,” he repeated.

“we’ll go now,” said the thinking machine. he left the room and returned a moment later dressed for the street. the slender, bent figure and the great head seemed more grotesque than ever.

“before we go,” he instructed, “telephone to your office and have a reliable man sent to watch the girl’s house. tell him under no circumstances to try to enter or speak with anyone there until he hears from us.”

the thinking machine stood waiting impatiently while hatch did this. then they took a cab to the tenement in south boston.

“dear me, what an old, ramshackle affair it is!” commented the scientist as they climbed the stairs.

the door of boyd’s room was not locked. the furniture and the personal effects of the man had been moved out — taken in charge by the medical examiner for possible use at an inquest.

“just how was this room fastened when boyd was found?” asked the scientist.

hatch showed him, at the door and windows. the thinking machine was interested for a moment and then looked out the side window. straight down fifteen feet was a wilderness of ash barrels and boxes and papers — a typical refuse heap of a cheap tenement. then the thinking machine squinted out the back window. there he saw an open space, a rough baseball diamond, intersected at two places by the trampled down rings of a circus.

perfunctorily he peered into the closet, after which his eyes swept the room in one comprehensive squint. he noted the begrimed condition of the place; the drooping cornice, the smoky ceiling, the gaping cracks in the floor, the rat holes beside the radiator, the dirty gas pipe leading down to a single jet. he leaned against a wall and wrote for several minutes on a sheet of paper torn from his notebook.

“have you an envelope?” he asked.

hatch produced one. the thinking machine put what he had written into the envelope, sealed it and handed it back.

“there’s something that may interest you some time,” he said, “but don’t open it until i give you permission to do so.”

“certainly not,” said the reporter, puzzled but without question. “but may i ask —”

“what it is?” snapped the scientist. “no, i will tell you when to open it.”

they descended the stairs together.

“somewhere to a public telephone,” were the thinking machine’s instructions to the cabby. at a nearby drug store, he disappeared into a telephone booth and remained for five minutes. when he came out he asked for the envelope he had given hatch and in a little crabbed hand wrote on it:

“november 9–10.”

“keep it,” he commanded, as he returned it to the reporter. “now we’ll drive to the girl’s place.”

when the cab reached the west end address it was a little later than dusk. caroline pierce and her girl chum occupied a front apartment on the ground floor. as the thinking machine and hatch were about to enter the building, tom manning, another reporter on hatch’s paper, approached them.

“the girl hasn’t returned,” he reported. “the other girl — miss jerrod — came back home from work just a few minutes ago.”

“we’ll see her,” said the thinking machine. then to manning: “at the end of two minutes, by your watch, after i enter this apartment, ring the bell several times. don’t be afraid. ring it! if any person runs out, man or woman, hold him. mr. hatch, you go to the back entrance of this apartment. stop any person, man or woman, coming from this suite.”

“you believe then —” hatch began.

“i’ll give you two minutes to get to the back door,” snapped the thinking machine.

hatch disappeared hurriedly, and for just two minutes, not a second more, the thinking machine waited. then he rang the bell of the apartment. miss jerrod appeared at the door. he followed her into the suite.

manning at the front door waited, watch in hand. when the two minutes were up he rang the bell time after time, long, insistent rings. he could hear it tinkling furiously. then he heard something else. it was the slamming of a door, a rush of feet and a struggle. then the thinking machine appeared before him.

“come in,” he said, modestly. “we have cunningham inside.”

5

a little drama of human emotion was being enacted in the tiny front suite. frank cunningham, wanted for the murder of fred boyd, sat wearily resigned in the corner furthest from the door under the watchful eye of hutchinson hatch. the man was unshaven, haggard, and there lay in his eyes the restless, feverish look of one who lives his life in terror of the law. caroline pierce, who was to have been his wife, had flung herself on a couch, weeping hysterically.

towering above the slender, shrinking figure of the thinking machine, miss jerrod was bitterly denouncing him for a trick which had given cunningham into his hands. the scientist listened patiently, albeit unhappily. he couldn’t help himself.

“you told me,” stormed miss jerrod, “that you believed him innocent, and now this — this.”

“well?” said the thinking machine meekly.

miss jerrod was about to say something else when cunningham stopped her with a gesture.

“i’m rather glad of it,” he said, “or rather i would be if it were not for her,” and he indicated caroline pierce. “i have never spent such hours of mortal fear as those since the murder of fred boyd. now, somehow, it’s a relief to know it must all come out.”

“you know you were a fool to try to hide, anyway,” said the thinking machine, frankly.

“i know i made a mistake — now,” replied cunningham. “but we were afraid — caroline and i— and i couldn’t help it.”

“well, go on with your story,” commanded the scientist testily.

manning, the other reporter, crossed the room and sat beside hatch, while cunningham moved over, took a seat beside the couch where the girl lay weeping and gently stroked her hair.

“i’ll tell what story i can,” he said at last. “i don’t know what you’ll think of it, but —”

“pardon me just a moment,” said the thinking machine. he went to cunningham and ran his long, slender fingers over the prisoner’s head several times. suddenly he leaned forward and squinted at cunningham’s head.

“what is this?” he asked.

“that is where a silver plate was put in,” cunningham replied. “i was badly injured by a fall when i was about fourteen years old.”

“yes, yes,” said the scientist. “go on with your story.”

“i have known boyd since we were boys together up in vermont,” cunningham began, “and there, too, i knew caroline. all three of us came from the same little town — caroline only two years ago. boyd and i had been in boston for seven years when she came. boyd lived for five years in that — that room in south boston, where —”

“never mind,” said the thinking machine. “go on.”

“well, caroline came here two years ago as i said and i believe that boyd loved her as well as i do,” said cunningham. “but she promised to be my wife and we were to be married next wednesday —”

“but the night boyd was killed,” interrupted the thinking machine impatiently. “come down to that.”

“i went to boyd’s room that night at a few minutes after eight o’clock. we sat for an hour or more and talked of our work, our plans and various things as we played cards — pinochle it was. neither of us was particularly interested in the game.

“boyd didn’t know of my coming marriage to caroline and finally i happened to mention her name. i also showed him the wedding ring i had bought that day for her. he looked at it, and asked me what i intended to do with it. i then told him that caroline and i were to be married.

“he was surprised. i think any man in his position would have been surprised, because i think it was his intention to ask her to marry him. well, at any rate, he grew angry about it, and i tried to placate him.

“i guess he was pretty hard hit — worse than i thought — for several times between the deals he picked up the ring and looked at it, then he’d put it down each time on his side of the table.

“after awhile he threw down his hand with the remark that he didn’t care to play. ‘now look here, fred,’ i said, ‘i didn’t think of the thing hitting you so hard.’ he replied something about it not being fair to him, though just what he meant i didn’t know.

“then word led to word, until finally i was in a fury at a careless reference he made to caroline — a thing he would never thought of doing in his proper senses — and demanded an apology. he grew ugly and said still more, and then, somehow, i don’t know quite what happened. i know that i had an insane desire to take hold of him — but —”

cunningham paused and gently stroked the hand of the girl.

“and then?” asked the thinking machine.

“you know this hurt on my head was more serious than you may imagine,” said cunningham. “there are times, in moments of anger particularly, when things are not clear to me. i lose myself, i don’t know what to do. a surgeon once explained to me why it was but i don’t remember.”

“i understand,” said the thinking machine. “go on.”

“well, from the moment the quarrel became really serious i would not swear to anything that happened,” cunningham resumed. “i know at last i found myself in the lower hall after what seemed a long time, and i remember leaving there, slamming the door behind me.

“i went down the avenue and was almost home when it occurred to me that the ring was in boyd’s room. by that time, too, i was seeing things more clearly. i wanted to go back and talk to boyd more calmly and see if both of us hadn’t said things we should not have said. it was with this double purpose of seeing him and getting the ring that i started back to the tenement.

“outside, i found a crowd. i wondered why, and asked. one man told me boyd had been murdered — choked to death; that the police knew who did it and were searching for him. i was terror-stricken, and after the body was taken out i walked away. the terror was on me, and after i turned into a side street i broke into a run. i knew myself, you see, and my own irresponsibility.

“then, although it was midnight, i came straight here, aroused caroline and miss jerrod and told them both what had happened so far as i knew. there seemed to be nothing else to do but hide; i did it. i remained here, as i thought safely enough. two or three reporters came and asked questions, and once a detective was here, but miss jerrod answered their inquiries satisfactorily and that seemed to be all — until now. tomorrow caroline and i were going back to vermont.”

there was a long pause. caroline pressed the hand of the man she loved to her cheek with a gesture of infinite confidence. the thinking machine sat silent with the tips of his long, slender fingers together.

“mr. cunningham,” he said at last, “you have not told us the one vital thing. did you or did you not kill fred boyd?”

“i don’t know,” was the reply. “if i only could know!”

“uh,” grunted the thinking machine. “i was afraid you wouldn’t know.”

6

hutchinson hatch and manning, the other reporter, gazed at cunningham thunderstruck, and from him to the thinking machine.

“don’t know whether or not you killed a man?” asked hatch incredulously.

“it’s perfectly possible, mr. hatch,” said the thinking machine, curtly. “i understand, mr. cunningham,” he explained. “i suppose you would be perfectly willing to go with me now?”

“no, no, no,” exclaimed caroline pierce suddenly, in evident terror.

“not to the police, miss pierce,” said the thinking machine. he paused a moment and looked at the girl curiously. of women he knew nothing, and knew he knew nothing. “perhaps it would assure you, miss pierce, if i told you i know that mr. cunningham did not kill boyd.”

“you believe he didn’t, then?” she asked eagerly.

“i know he didn’t,” said the thinking machine tersely. “two and two make four not some times, but all the time,” he went on enigmatically. “if mr. cunningham will come with me now we will establish beyond all doubt the cause of boyd’s death. do you believe me?”

“yes,” said the girl slowly, and she looked steadily into the squint eyes of the scientist. “i— i have faith in you.”

the thinking machine coughed, slightly embarrassed, and turned to hatch with a faint color in his cheeks.

“well, who did kill boyd?” asked hatch, amazed.

“that’s what we will now demonstrate,” was the reply. “come on.”

after cunningham had himself assured the girl of his safety the four men passed out into the night — it was nearly 10 o’clock — entered a cab and were driven to the tenement in south boston. there they passed up the one flight of stairs into the room where boyd had been found, and after lighting the gas the scientist made one quick survey of the room.

“these walls are awfully thin,” he commented petulantly. “if i should fire a pistol in here i might kill someone in another room. yes, a knife would do better. have any of you gentlemen a knife — one with a blade that won’t break easily?”

“will this do?” asked cunningham, and he produced one.

the thinking machine examined it and nodded his satisfaction.

“now a revolver,” he said.

manning went out to get one. while he was gone the thinking machine gave some formal instructions to cunningham and hatch.

“i’m going to put out this light and remain in this room alone,” he said. “i may be here fifteen minutes or i may be here till daylight. i don’t know. but i want you three to remain quietly outside the door and listen. when i need you i shall need you quickly. my life may be in danger, and i am not a strong man.”

“what is it anyway?” asked hatch curiously.

“after awhile you will hear something inside, i have no doubt,” went on the scientist, paying no attention to the question. “but don’t enter the room under any circumstances until i call out or you hear a struggle.”

“but what is it?” asked hatch again. “i don’t understand at all.”

“i’m going to find the murderer of fred boyd,” said the scientist. “please do not ask so many absurd questions. they annoy me exceedingly. i may have to kill him,” he added reflectively.

“kill him?” gasped hatch. “who, the murderer?” he couldn’t help it.

“yes, the murderer,” was the tart reply.

manning returned with the revolver, which the thinking machine examined and handed to hatch.

“you will know what to do with it when you enter the room,” he instructed. “you, manning, come in with these other two and light this gas. keep your matches in your hand.”

then the two reporters and cunningham passed out of the room, closing the door, but not fastening it. pressed close against the panels outside, listening, hatch started to explain to manning in a whisper when they heard the irritated voice of the scientist.

“keep silent,” was the sharp command.

five minutes, ten minutes, half an hour of utter silence, save for a distant sound of some sort in the big tenement. but no one came up the stairs. the dim gas light fluttered weirdly down the hall.

a full hour passed, still nothing. hatch could hear his heart beat, also he thought the regular breathing of the thinking machine. at last there came a slight sound, and hatch started. the other men heard, too.

it was a faint whispering sound, as of the wind rustling through dead leaves, or the silken swish of skirts or the gasp of a dying man.

hatch clutched the revolver more firmly and set his teeth hard together. he was going to face something — a deadly, terrible something — and had not the faintest idea of what it might be. manning held a match ready for instant use.

then, as they listened, there was another sound, still faint, as of something sliding over the floor. suddenly there was a heavy thump, a half-strangled cry from the thinking machine and the sounds of a fearful struggle. hatch rushed into the room with revolver raised; manning was just behind him. a match flared up and they saw a struggling heap on the floor. the arm of the scientist rose and fell thrice, burying the knife each time in flesh.

in the light of the gas, which hissed into a brilliant light under the match, the reporter placed the revolver flat against the head of a writhing, twisting body and fired. for the second time he fired, and the struggling bodies lay still.

then for the first time hatch realized what had happened. a giant boa constrictor held the thinking machine in its coils and was in its death struggle almost crushing the life out of him. it required the combined efforts of the three men to release the scientist from the deadly folds. he lay still for a moment, but finally the life came back into his frail body with a rush. he raised up from hatch’s arms and looked curiously at the snake.

“dear me, dear me,” he commented. “what a brain would have been lost to scientific inquiry if that snake had killed me.”

occupants of the house, aroused by the two pistol shots, rushed again terror-stricken to the room, and after awhile the police came and rescued the four men from the besieging mob of questioners. all went to the police station, and there the thinking machine, with several caustic comments on the police in general, told his story. the body of the giant retile lay full length on the floor.

“mr. hatch here asked for my advice in the matter,” he explained to the police captain, “and i did what i could to assist him. when he explained the condition of the body and the room when it was broken open — the fact the door and both windows were fastened securely inside — it instantly occurred to me that, with suicide removed as a possibility, the thing which had killed boyd was still in the room or else had escaped only after the body was found.

“it was not unreasonable to suppose that any animal, a snake for instance, would have attempted to leave the room while a crowd of people blocked the door; in fact it was not unreasonable to suppose that such a snake, snuggly fixed in a large, tumble-down building, with the infinite possibility of feeding on rats and mice, would attempt to leave the building at all. it could get water easily from a dozen places.

“therefore i presumed it was a snake, and i asked mr. hatch to ascertain for me first if the people in the house had ever been greatly annoyed by rodents; if they were now, and if not, when they had noticed that they were not. he reported to me that they had been annoyed up to a fortnight preceding the crime, but since they had not noticed. of course a boa constrictor can live on rodents, therefore they would leave the building or be eaten out of it gradually.

“a fortnight since they missed the rodents? that meant that the snake must have been in the building at least that long. all these conclusion i reached before i personally went over the scene. if it were a snake, as i thought possible, it must have come from somewhere. where, then?”

the thinking machine paused and looked from one to another of his hearers. each in turn shook his head, hatch being the last to do so.

“and yet your own paper published a full solution of the mystery before it ever occurred,” said the scientist sharply. “looking from the back window of the room there, perfectly visible, were three banked rings, plainly where a circus had been. possibly the snake escaped from that circus and crept into the house.

“i called up your office on the ‘phone, mr. hatch, and ascertained that there had been a circus on that place two weeks before, november 9 and 10, and further i found that a boa constrictor had escaped from that circus. you printed a column of it on the first page.”

“lord, and we really thought that was a press agent’s yarn,” remarked hatch sadly.

“tonight when we went to the room it was my intention to allow the snake to creep out of that large hole near the radiator — i suppose you noticed there was one there? — then to pass between the snake and the hole and call for mr. hatch and these other gentlemen who were waiting outside the door. if the snake attacked me i had a knife and mr. hatch had a revolver.

“but i’m afraid i didn’t give the snake credit for quickness and such enormous strength,” he went on ruefully. “i heard the snake come out of the hole, and then instantly almost i felt its folds crushing me. then these gentlemen rushed in. i can readily understand how it choked boyd, he having no way to defend himself, and then crawled away when those people knocked on the door. it nearly crushed the life out of me.”

that seemed to be all, and the thinking machine stopped.

“but frank cunningham?” asked the police captain. “why did he run away, and where is he now?”

“cunningham?” repeated the scientist, puzzled.

“yes,” said the captain. “where is he?”

“why here he is,” and the thinking machine indicated the accused man. “mr. cunningham permit me to introduce you to captain — er — er. i don’t know his name.”

the captain was not surprised; he was nonplussed. it had never occurred to him to ask the name of the fourth member of the party; he knew the two newspaper men.

“how — where — when did you —” he began.

“not knowing whether or not he had killed his friend boyd,” explained the scientist, “he was hiding in the suite of miss caroline pierce, his fiance. his lack of knowledge was due entirely to a queer mental condition. he was badly hurt at one time and wears a silver plate in his head. that accounts for many things.”

“how did you get him?” asked the captain, amazed.

“i walked into miss pierce’s suite after i had put a man at the back and front to stop any one who ran out, and told miss pierce’s friend, miss jerrod, that i believed — in fact knew — that cunningham was innocent, and that i had come merely to warn him,” said the thinking machine.

“i told her then that three policemen were at the front door, and then mr. manning here rang the bell violently, as i had instructed him, and cunningham dashed out of a rear room and started out the back way. mr. hatch got him there. it was perfectly simple — that part of it. of course, there was a chance that he wasn’t there at all — but he was.”

the thinking machine arose.

“is that all?” he asked.

“why did you examine cunningham’s head before he told us his story?” asked hatch.

“i have some idea of the cranial formation of criminals and i merely wanted to satisfy myself,” said the scientist. “it was then that i discovered the silver plate in his head.”

“and this?” asked hatch. he took from his pocket the sealed envelope which the thinking machine had given him in the tenement room immediately after he had inspected the room. on this envelope was written “november 9–10”, this being the date the circus was in south boston.

“oh, that?” said professor van dusen a little impatiently, “that is merely a solution to the mystery.”

hatch opened the envelope and looked at it. there were only a few words:

“snake. came through hole near radiator. lived in walls. escaped from circus. cunningham innocent.”

“that all?” again asked the thinking machine.

there was no answer, and the scientist and the two newspaper men left the police station, followed by cunningham.