It was nearly a week after the events last narrated before I saw Maitland again, and then only by chance. We happened to meet in the Parker House, and, as he had some business pertaining to a case he was on, to transact at the Court House, I walked up Beacon Street with him. There is a book or stationery store, on Somerset Street, just before you turn down toward Pemberton Square. As we were passing this store, Maitland espied a large photographic reproduction of some picture.

“Let us cross over and see what it is,” he said. We did so. It was a photograph of L. Alma-Tadema’s painting of Antony and Cleopatra. Maitland started a little as he read the title, and then said lightly: “Do you suppose, Doc, that woman’s mummy is in existence? I should like to find it. I’ve an idea she left some hieroglyphic message for me on her mummy-case, and doesn’t propose to let me rest easy until I find and translate it. Now, if I believed in transmigration of souls—do you see any mark of Antony about me? Say, though, just imagine the spirit of Marcus Antonius in a rubber apron, making an analysis of oleomargarine! But here we are; good-bye,” and he left me without awaiting any reply. He seemed to me to be in decidedly better spirits than formerly, and I was at the time at a loss to account for it. The cause of his levity, however, was soon explained, for that night, as Gwen, my sister, and I were sitting cosily in the study according to our usual custom, Maitland walked in, unannounced. He had come now to be a regular visitor, and I invented not a few subterfuges to get him to call even oftener than he otherwise would, for I perceived that his coming gave pleasure to Gwen. She exhibited less depression when in his presence than at any other time. I had learned that hers was one of those deep natures in which grief crystallises slowly, but with an unconquerable persistence. Instead of her forgetting her bereavement, or the sense thereof waxing weaker by time, she seemed to be drifting toward that ever-present consciousness of loss in which the soul feels itself gradually, but surely, sinking under an insupportable burden—a burden so long borne, so well known, that the mind no longer thinks of it. The heart beats stolidly under its load, and seems to forget the time when it was not so oppressed. No one knows better than we physicians the danger of this autocracy of grief, and I watched Gwen with a solicitude at times almost bordering on despair. But, as I said before, she always seemed to show more interest in affairs when Maitland was present, and, on the night in question, his abrupt and unexpected entrance surprised her into the betrayal of more pleasure than she would have wished us to note, and, indeed, so quickly did she conceal her confusion that I was the only one who noticed it. Maitland was too busy with the news he brought.

“Well, Miss Darrow,” he began at once, “at last your detective has got a clue—not much of a one—but still a clue. I can pick the man for whom we are looking from among a million of his fellows—if I am ever fortunate enough to get the chance.”

Somebody has already called attention to the fact that women are more or less curious, and there are well-authenticated cases on record where this inquisitiveness has even extended to things which did not immediately concern themselves; so I have little doubt I shall be believed when I say the women folk were in a fever of expectancy, and besought Maitland with an earnestness quite unnecessary—(it would have required a great deal to have prevented his telling it)—to begin at the beginning, and relate the whole thing. He readily acceded to this request, and began by telling them the experiences which I have just narrated. It was, he said, during the last act of Sardou’s “Cleopatra” that the idea had suddenly come to him to change the plan of search from the analytical to the synthetical.

“You see,” he continued, “I had from the first been trying to find the assassin without knowing the exact way in which the crime was committed. I now determined to ascertain how, under the same circumstances, I could commit such a crime, and leave behind no other evidences of the deed than those which are in our possession. I began to read detective stories, with all the avidity of a Western Union Telegraph messenger, and, of course, read those by Conan Doyle. The assertion of ‘Sherlock Holmes’ that there is no novelty in crime; that crimes, like history, repeat themselves; and that criminals read and copy each other’s methods, deeply impressed me, and I at once said to myself: ‘If our assassin was not original, whom did he copy?’

“It was while reading ‘The Sign of the Four,’ which I had procured at the Public Library, that I made the first discovery. The crime therein narrated had been committed in such a singular manner that it at once attracted my attention. The victim had apparently been murdered without anyone having either entered or left the room. In this respect it was like the problem we are trying to solve. Might not this book, I said to myself, have suggested to your father’s assassin the course he pursued. I concluded to go to the library and ask for a list of the names of persons who had taken out this book for a few months prior to your father’s death. I was fully aware that the chance of my learning anything in this way was very slight, In the first place; I reasoned that it was not especially likely your father’s murderer had read ‘The Sign of the Four,’ and, in the second place, even if he had, what assurance had I that he had read this particular copy of it? Notwithstanding this, however, I felt impelled to give my synthetical theory a fair experimental trial. I was informed by the Library attendants that the book had been much read, and given the list of some twenty names of persons who had borrowed the book during the time I had specified. With these twenty-odd names before me, I sat down to think what my next step should be. I went carefully over this chain of reasoning link by link. ‘I wish to find a certain murderer, and have adopted this method in the hope that it may help me. If I derive any assistance at all from it, it will be because my man has read this particular copy of this work; therefore, I may as well assume at the start that among these twenty-odd names is that of the man I want. Is there any possibility of this crime having been committed by a woman?’ was my next question, and my answer was, ‘Yes, a possibility, but it is so decidedly improbable that I may count it out for the time being.’ Accordingly, I set aside all the female names, which cut my list down to eighteen. Several of the applicants had only signed the initials of their given names, and the attendant, copying them from the slips, had done likewise; so I was obliged to go to the registration clerk to determine this question of sex, and, while there, I also ascertained the age of each applicant—that is, of all but two. The registrar could give me no information regarding J. Z. Weltz, or B. W. Rizzi. When I told him that one of the clerks had copied the names for me from application slips, he informed me that if I would go back to her I would undoubtedly find she had taken the two last-mentioned names from the green slips used in applying for books for hall use, as neither J. Z. Weltz nor B. W. Rizzi was a card-holder.

“I decided to let these two names rest a while, and to give my attention to the others. After careful deliberation I felt reasonably sure your father’s assassin could not fail to be a man of mature judgment and extraordinary cunning, probably a man past middle life—at all events, I could safely say he was over twenty-one years of age. Proceeding upon this assumption my list was reduced to ten names. But how should I further continue this process of exclusion? This was the question which now confronted me. I could think of but one way, apart from personally making the gentlemen’s acquaintance, which I did not then wish to do, and that was to ascertain what other books they had borrowed immediately before and after they had read ‘The Sign of the Four.’ This was the course I determined to pursue.

“If you ask me why I so persistently followed an investigation, a successful outcome of which anyone must recognise would be little short of miraculous, I can only say that I felt impelled to do so. Perhaps the impulse was due to my habit of testing patiently and thoroughly each new theory which impresses me as having any degree of probability, and perhaps it was due to something else—Cleopatra, perhaps, eh, Doctor?—I don’t know. I determined, however, to thoroughly satisfy myself regarding these ten men. I made a careful list, with the assistance of an attendant, of ten books taken by each man, five taken just prior to ‘The Sign of the Four,’ and the other five just following it. I made no deductions until the list was completed, although I began to see certain things of interest as we worked upon it. At length the whole hundred titles were spread before me, and I sat down to see what I could make of them. I purposely reserved consideration of the books borrowed by Weltz and Rizzi until the last, because I had been able to learn nothing of them, and considered, therefore, that they were the most difficult persons in the list about whom to satisfy myself. I found the other eight exhibited no system in their reading. One had read—I think I can remember the books in the order in which they were borrowed—‘Thelma,’ ‘Under Two Flags,’ ‘David Copperfield,’ ‘The Story of an African Farm,’ ‘A Study in Scarlet,’ ‘The Sign of the Four,’ ‘The Prisoner of Zenda,’ ‘The Dolly Dialogues,’ ‘The Yellow Aster,’ ‘The Superfluous Woman,’ and ‘Ideala.’ This is a fair sample of the other seven. Not so, however, with Messrs. Weltz and Rizzi. The reading of these men at once impressed me as having a purpose behind it.

“I will read you a list of the books taken by Weltz and Rizzi, just to see what you will make out of it:

“There, do you wonder that the perusal of that list excited me? Come, now, before I go any further, tell me what you make of it, Doc,” and he passed it to me.

“There seems to me to be a singular unanimity of purpose existing between these two men,” I said; “not only as regards the subject-matter of their reading, but in no less than six cases they have both perused the same volume. This never happened by chance. Clearly, they are acquaintances, and are working together toward some common end. I should think it very likely, judging from their interest in cancers and toxicology, that they were medical students. Numbers four and five don’t exactly seem to strengthen my medical hypothesis, but they are only two out of the ten. That’s about all I can make out of it;” and I returned the list to him.

“Your views in the matter,” replied Maitland, “are precisely those which first occurred to me, and I am not sure but I should still hold them, had I been obliged to decide solely from the evidence I have submitted to you. It was clear to my mind from the first that some common purpose actuated both Weltz and Rizzi. With a view to ascertaining where they lived as a preparatory step toward learning more of them, I consulted a Boston directory, only to learn that it contained no such names. I was about to examine some of the directories of neighbouring towns when it occurred to me that the easiest way to find their places of residence would be to consult the green slips upon which they had procured their books, and I accordingly asked the attendant to kindly let me look at them. While she was collecting the slips I re-examined the list of books taken by Weltz and Rizzi, especially those which had been taken by both men. One thing at once struck my attention, and that was that most of these latter were large books which would take a long time to peruse and would require to be borrowed several times for hall use, were they to be examined with any care. I put this fact down for future reference and gave my attention to the green slips, the whole twenty of which the attendant now placed before me. The residence of Weltz was given as No. 15 Staniford Place, Boston, while that of Rizzi was No. 5 Oak Street, Boston. I was about to walk over to Oak Street to see if Rizzi were still there when, in returning the slips to the attendant, I noticed a peculiarity in Weltz’s ‘z’ which I had thought I had seen in Rizzi’s signature. I immediately compared the slips. There was the same oddly shaped ‘z’ in both. It was made like this”—and he handed us a slip of paper with this z* upon it.

“You see,” he continued, “it is so unusual a way of making the letter that it at once attracted my attention, notwithstanding the fact that Rizzi wrote with his left hand. Closer examination revealed other peculiarities, as in the r*’s, common to both hands. Well, to make a long story short, I satisfied myself that the same person wrote the whole twenty slips and was, moreover, ambidextrous. This I considered as a very promising discovery, so much so, indeed, that I gave up an engagement I had for the evening and decided to camp right there until the Library closed. Happily the books I had been consulting were still on the table. I picked out those borrowed under the names of Weltz and Rizzi, and began a most careful examination of them. I had been working about two hours when I discovered something that fairly took my breath away. I was not sure that I was right, but I knew that, if my microscope bore me out, I would be able to stake my life that the murderer of John Darrow had read that book. I was aware, however, that even then I should not be able to name the man who had put his mark upon the book, but I could take oath that the record was made by the same hand that committed the murder.

***** Transcriber’s note: the symbols designated z* and r* are shown as script which is not reproducible here. *****

“I was too excited to do more till this had been settled, so I besought the official in charge to let me take all the books home with me, if only for a day, explaining to him the vital importance of my request. He readily consented and I hastened home with the whole lot. You may imagine with what interest I put the page I wished to examine under my microscope and laid beside it the piece of glass which, you will perhaps remember, I cut from a window of the room in which the murder was committed. I believe I have never yet explained to Miss Darrow why I preserved that bit of glass. There were two reasons for it. The house had been primed that day and there were two smutches of paint upon the glass and two almost identical smutches upon the sill. One was a sinuous line, as if the glass had been struck with a short bit of rope,—or possibly rubber tubing since no rope-like texture was visible,—which had previously been soiled with the paint from the sill. The other mark was that of a human thumb. I had seen at the World’s Fair an exhibit of these thumbmarks collected by a Frenchman who has made an exhaustive study of the subject, and had learned there for the first time that no two thumbs in the world can make the same mark. I knew, therefore, that this slip of glass would at any time tell me whether or not a suspected man were guilty. I had not failed to get the thumb-marks of the men who painted the house on that day, as well as those of every other person known to be about the place. The marks upon the glass could not, by any possibility, have been made by any of them. The deduction was inevitable. They were made by the man who stood by the window when the murder was committed.

“You will be surprised when I tell you it was some moments before I could summon up courage to look through my microscope upon the page beneath it. You see, I had been seized by an unaccountable conviction that I had at last found a real clue to the murderer, and I dreaded lest the first glance should show this to have been an idle delusion. At length I looked. The thumb that had pressed the paper was the thumb that had pressed the glass! There was not a doubt of it. My suspicions were confirmed. Everything now regarding this book was of immense importance. The page upon which the mark was found—well, I think you would open your eyes if I were to read it to you. I will defer this pleasure, however, till I see if my suspicions are correct. The thumb-mark is upon page 469 of ‘Poisons, Their Effects and Detection,’ by Alexander Wynter Blyth.

“No sooner had I made sure of my discovery than I set out for No. 5 Oak Street, the address given by Rizzi. There was no such person there, nor had there been anyone of that name in the house during the three years of the present tenant’s occupancy. I went to 15 Staniford Place with the same result. A young woman about twenty-five years of age came to the door. She informed me that she had been born in the house and had always lived there. She had never known anyone by the name of Weltz. This was just what I had expected. The man for whom we are searching is shrewd almost beyond belief, and if we succeed in finding him it will not, we may be assured, be the result of any bungling on his part.

“I have now told you all I have learned, or rather all that is sufficiently definite to communicate—it is not much, yet it is a clue and may serve to give our hope a new lease of life. What do you think of it, Miss Darrow?”

“I think what you have learned,” Gwen replied, “will be of the utmost importance. You have now something definite to guide you. I am most fortunate in having the services of such a detective,—indeed, I am at a loss to know how to thank you for all you have done,—for all you are doing, I—”

“My dear Miss Darrow,” Maitland interrupted, “I need no thanks. Be assured I am selfish in all I do. It is a pleasure to me, therefore I do it. You see I deserve no credit. If I am able to free you from the danger of sacrificing yourself, I shall be more than repaid.”

Gwen made no reply, but I, sitting as I did close beside her, saw the moisture gather between her drooping lids. Maitland took his leave almost immediately, having, he said, a long evening’s work before him; while Gwen, Alice, and I discussed the news he had brought us, until far into the night. I did not see him the next day, which was Tuesday, and I believe not on Wednesday. It was Thursday afternoon, if I do not mistake, that he sent me a note asking me to call on him at his office. I went at once, thinking it might be something very important. I found him alone and waiting for me.

“I wanted,” he began as soon as I was seated, “to talk this matter over with you. You see the great difficulty which besets me in this case is that nearly all our evidence, while it is of a nature to enable us to convict our man once we have him, is yet of almost no assistance to us in finding him. What do we know of him up to date; or at least of what do we feel reasonably assured? Let us see. John Darrow was poisoned in some mysterious way by a man who was stationed just outside the partly opened window. The weapon, or whatever was used as such, was taken away by the murderer. Nothing in the nature of a projectile could have been employed, since the wound was upon a part of the victim’s throat known to have been turned away from the window and to have been completely shielded upon that side by the high and massive back of the chair in which the victim sat.

“He was fully eight feet from the casement, so that the assassin could not have reached in and struck him. There were no footprints by the window, as the assassin had strapped small boards upon his feet. It is most likely, therefore, that he has some peculiarity about his feet which he thought best to conceal. He is about five feet five inches tall, weighs about one hundred and thirty-five pounds, and steps three or four inches longer when the right foot is thrown forward than he does when the left foot leads. We have a cast of the assassin’s hand showing unmistakable evidence of the habit of biting the nails, with the exception of that of the little finger, which nail, by the way, is abnormally long, and could only have been spared for some special reason. The murderer is most likely a foreigner. His handwriting would indicate this even if we did not know, from the books he read, how conversant he is with at least one foreign tongue. Again, he has some decided interest in the subject of cancers and, perhaps, some interest in legerdemain, if we may judge from his perusal of Robert Houdin’s book.

“There are one or two other things I have learned, but this, so far as any present effect is concerned, is about all we know, and it doesn’t seem to make the conduct of our search a very easy matter. We have clearly to deal with a man who is possessed not merely of low criminal cunning, but, I have reason to believe, with one who has education and culture, and, if anything can be judged from handwriting, rare strength of character as well. If we could only find some motive! No one but a maniac would do such a deed without a motive, yet we can’t find one. A maniac! By Jove! I hadn’t thought of that. What do you think of the idea? ‘Though this be madness, yet there is method in’t,’ eh?”

I told him that the maniac theory did not appeal to me very strongly. “Madness, to be sure, is often exceedingly cunning,” I said, “but it is hardly capable of such sustained masterfulness as our criminal has evinced.”

“Look here, Doc,” Maitland said, breaking out suddenly, “I’ve an idea. Might not this fellow’s interest in cancers be due to his having one himself? Suppose you make a canvass of the specialists on cancer in Boston and vicinity, and see if any of them remember being consulted by a patient answering the description with which I will provide you. In addition to this I will insert an ad in the papers calling attention to a new method for the cure of cancer, and asking all interested to call at your office for further particulars. The plan does not promise much, still it may bring him. What do you say?”

I expressed my willingness to do all in my power to aid him, and he left me. The next morning’s papers contained the advertisement and I had several calls in answer to it. These would have caused me much inconvenience had I not explained the whole ruse in confidence to a medical friend who made a specialty of the treatment of cancers, and persuaded him to come to my office during the hours specified in the advertisement. When a patient would call I would satisfy myself that it was neither the person we were searching for, nor anyone sent by him to make inquiries, and then turn him over to my colleague, Dr. Rhodes. It would never have occurred to me to interest myself in any patient who did not answer the description given me by Maitland, had he not especially cautioned me in this regard.

“We have,” he said, “to deal with a man possessed of ability of no common order. We have already seen that he never runs a risk, however slight, which he can avoid. It is more than likely, therefore, if our advertisement meets his eye and interests him, he will inquire into it through some second party. Again, we are by no means certain that his interest in cancers is a purely personal one. Perhaps it is a wife, a sister, or some other relative who is afflicted. In this case we could hardly expect him to come himself. Let me caution you, therefore, to closely scrutinise all applicants and question them until you are satisfied they are in nowise connected with the man for whom we are searching.”

I followed this advice most carefully and had no difficulty in convincing myself that none of my callers had any relation whatsoever with the murderer of John Darrow. This order of things was continued for several days with the same result. In the meantime Maitland was working upon a new clue he had discovered. He would tell me all about it, he said, when he had followed it to the end. This was on Tuesday. On Friday he came to the house and informed us that he had met a man who had known a M. Henri Cazot, a Frenchman whose description seemed to tally perfectly with nearly all we knew of Mr. Darrow’s murderer.

“It came about in this way,” Maitland began in response to Gwen’s request that he should tell us all about it: “I determined to thoroughly search every book on the ‘Weltz-Rizzi’ list, to see if I might not get some additional clue. In the work by Robert Houdin entitled ‘The Sharper Detected and Exposed’ I found the statement that gamblers often neutralised a cut in a pack of cards by a rapid and dexterous sleight. This, the book went on to say, was accomplished in the following manner: When the cards are cut and left in two packets upon the table, the sharper picks up with his right hand the parcel of cards which was originally at the bottom of the pack. This is brought above the other packet, as in an honest cut, but, just before releasing the cards, the lower parcel is deftly tilted up by inserting the right little finger under it, and the upper packet quickly slid beneath it, leaving the cards in precisely the position they occupied before cutting; For this purpose, the book continued, the nail of the right little finger is worn very long, so as to facilitate its being thrust beneath a packet of cards. Here, I said to myself, is a possible explanation of one of the peculiarities of my plaster cast. The long nail on the left little finger may have served its function at the gaming table. If so, however, it would seem to indicate that our man is left-handed, while, as we have already seen, the writing upon the library slips would indicate that he is ambidextrous. We need not, therefore, I reasoned, be surprised if we find that both little fingers have long nails. I at once acted upon these thoughts and began a search of the gambling resorts of this city. In order not to excite suspicion I played a little in each place, watching my opportunity to engage the proprietor in conversation. In every case I followed the same formula. Did he remember the gentleman who used to come there? Foreigner,—spoke French, a little under medium height; had a sort of halt in his walk; bit his finger nails, etc., etc. I met with no encouragement in the down-town places, though the proprietor of one of the Hayward Place ‘dives’ had an idea such a man had been there, but only once or twice and he was not sure he could place him. I then went up to the South End and on Decatur Street found a man who promptly responded to my inquiries: ‘Gad! that’s Henri Cazot fast enough, in all but the height and gait. Dick there, he’ll tell you all about him. He owes him a little debt of honour of about a hundred plunks. He gave him his note for it, and Dick carries it around with him, not because he thinks he’ll ever get it, but he likes the writing. M. Henri Cazot! eh, Dick?’ and he burst into a coarse laugh. I turned to Dick for further information. He had already produced a much-crumpled paper and was smoothing it out upon the table.

“‘There’s the article,’ he said, bringing his hand down emphatically upon it. ‘The cuss was hard up. Luck had gone agin him and he had lost every cent he had. Jem Macey was a-dealin’ and Cazot didn’t seem to grasp that fact, but kept bettin’ heavy. You see, young feller, ye ain’t over likely to win at cards when yer playin’ agin the dealer. Cazot didn’t know this and I wouldn’t tell him, for he was rather fly with the cards himself when he wan’t watched too close. Well, he struck me for a loan; said his little girl was hungry and he hadn’t a cent to buy bread. Gad, but he looked wild though! I always thought he was more’n half loony. Well, as I had helped to fleece him I lent him a hundred and took this here note. That’s the last I ever see of M. Henri Cazot,’ and he handed the paper to me. I glanced at the signature. It was the same hand that had written ‘Weltz’ and ‘Rizzi’ upon the library slips. There was that unmistakable z and the peculiar r which had just attracted my attention! It required considerable effort on my part to so restrain my feelings as not to appear especially interested in what I had learned. I think, however, I succeeded, as they freely answered my questions regarding Cazot and the daughter of whom he had spoken. They knew nothing further, they said, than what they had told me.

“‘It was a year ago come next month that I lent him the money,’ my informant continued. He pocketed it, hurried out, and that is the last I have ever seen or heard of him. Shouldn’t wonder if he’d blown his brains out long ago. He used to have a mighty desperate look at times. He was one of them Monte Carlo fellers, I reckon.’

“That’s all I have been able to learn thus far. It isn’t very much, but it shows we are on the right track. By the way, Doc, I’m going to change that ad to-morrow, offering treatment by letter. Perhaps our man is too shy to apply in person. At all events we’ll give the other method a trial.”