Mr. Sherlock Holmes was always of opinion that I should publish the singular facts connected with Professor Presbury, if only to dispel once for all the ugly rumours which some twenty years ago agitated the University and were echoed in the learned societies of London. There were, however, certain obstacles in the way, and the true history of this curious case remained entombed in the tin box which contains so many records of my friend's adventures. Now we have at last obtained permission to ventilate the facts which formed one of the very last cases handled by Holmes before his retirement from practice. Even now a certain reticence and discretion have to be observed in laying the matter before the public.

It was one Sunday evening early in September of the year 1903 that I received one of Holmes's laconic messages: "Come at once if convenient—if inconvenient come all the same.—S.H." The relations between us in those latter days were peculiar. He was a man of habits, narrow and concentrated habits, and I had become one of them. As an institution I was like the violin, the shag tobacco, the old black pipe, the index books, and others perhaps less excusable. When it was a case of active work and a comrade was needed upon whose nerve he could place some reliance, my role was obvious. But apart from this I had uses. I was a whetstone for his mind. I stimulated him. He liked to think aloud in my presence. His remarks could hardly be said to be made to me—many of them would have been as appropriately addressed to his bedstead—but none the less, having formed the habit, it had become in some way helpful that I should register and interject. If I irritated him by a certain methodical slowness in my mentality, that irritation served only to make his own flame-like intuitions and impressions flash up the more vividly and swiftly. Such was my humble role in our alliance.

When I arrived at Baker Street I found him huddled up in his arm-chair with updrawn knees, his pipe in his mouth and his brow furrowed with thought. It was clear that he was in the throes of some vexatious problem. With a wave of his hand he indicated my old arm-chair, but otherwise for half an hour he gave no sign that he was aware of my presence. Then with a start he seemed to come from his reverie, and, with his usual whimsical smile, he greeted me back to what had once been my home.

"You will excuse a certain abstraction of mind, my dear Watson," said he. "Some curious facts have been submitted to me within the last twenty-four hours, and they in turn have given rise to some speculations of a more general character. I have serious thoughts of writing a small monograph upon the uses of dogs in the work of the detective."

"But surely, Holmes, this has been explored," said I. "Bloodhounds—sleuth-hounds——"

"No, no, Watson; that side of the matter is, of course, obvious. But there is another which is far more subtle. You may recollect that in the case which you, in your sensational way, coupled with the Copper Beeches, I was able, by watching the mind of the child, to form a deduction as to the criminal habits of the very smug and respectable father."

"Yes, I remember it well."

"My line of thoughts about dogs is analogous. A dog reflects the family life. Whoever saw a frisky dog in a gloomy family, or a sad dog in a happy one? Snarling people have snarling dogs, dangerous people have dangerous ones. And their passing moods may reflect the passing moods of others."

I shook my head. "Surely, Holmes, this is a little far-fetched," said I.

He had refilled his pipe and resumed his seat, taking no notice of my comment.

"The practical application of what I have said is very close to the problem which I am investigating. It is a tangled skein, you understand, and I am looking for a loose end. One possible loose end lies in the question: Why does Professor Presbury's faithful wolf-hound, Roy, endeavour to bite him?"

I sank back in my chair in some disappointment. Was it for so trivial a question as this that I had been summoned from my work? Holmes glanced across at me.

"The same old Watson!" said he. "You never learn that the gravest issues may depend upon the smallest things. But is it not on the face of it strange that a staid, elderly philosopher—you've heard of Presbury, of course, the famous Camford physiologist?—that such a man, whose friend has been his devoted wolf-hound, should now have been twice attacked by his own dog? What do you make of it?"

"The dog is ill."

"Well, that has to be considered. But he attacks no one else, nor does he apparently molest his master, save on very special occasions. Curious, Watson—very curious. But young Mr. Bennett is before his time, if that is his ring. I had hoped to have a longer chat with you before he came."

There was a quick step on the stairs, a sharp tap at the door, and a moment later the new client presented himself. He was a tall, handsome youth about thirty, well dressed and elegant, but with something in his bearing which suggested the shyness of the student rather than the self-possession of the man of the world. He shook hands with Holmes, and then looked with some surprise at me.

"This matter is very delicate, Mr. Holmes," he said. "Consider the relation in which I stand to Professor Presbury, both privately and publicly. I really can hardly justify myself if I speak before any third person."

"Have no fear, Mr. Bennett. Dr. Watson is the very soul of discretion, and I can assure you that this is a matter in which I am very likely to need an assistant."

"As you like, Mr. Holmes. You will, I am sure, understand my having some reserves in the matter."

"You will appreciate it, Watson, when I tell you that this gentleman, Mr. Trevor Bennett, is professional assistant to the great scientist, lives under his roof, and is engaged to his only daughter. Certainly we must agree that the Professor has every claim upon his loyalty and devotion. But it may best be shown by taking the necessary steps to clear up this strange mystery."

"I hope so, Mr. Holmes. That is my one object. Does Dr. Watson know the situation?"

"I have not had time to explain it."

"Then perhaps I had better go over the ground again before explaining some fresh developments."

"I will do so myself," said Holmes, "in order to show that I have the events in their due order. The Professor, Watson, is a man of European reputation. His life has been academic. There has never been a breath of scandal. He is a widower with one daughter, Edith. He is, I gather, a man of very virile and positive, one might almost say combative, character. So the matter stood until a very few months ago.

"Then the current of his life was broken. He is sixty-one years of age, but he became engaged to the daughter of Professor Morphy, his colleague in the chair of Comparative Anatomy. It was not, as I understand, the reasoned courting of an elderly man, but rather the passionate frenzy of youth, for no one could have shown himself a more devoted lover. The lady, Alice Morphy, was a very perfect girl both in mind and body, so that there was every excuse for the Professor's infatuation. Nonetheless, it did not meet with full approval in his own family."

"We thought it rather excessive," said our visitor.

"Exactly. Excessive and a little violent and unnatural. Professor Presbury was rich, however, and there was no objection upon the part of the father. The daughter, however, had other views, and there were already several candidates for her hand, who, if they were less eligible from a worldly point of view, were at least more of an age. The girl seemed to like the Professor in spite of his eccentricities. It was only age which stood in the way.

"About this time a little mystery suddenly clouded the normal routine of the Professor's life. He did what he had never done before. He left home and gave no indication where he was going. He was away a fortnight, and returned looking rather travel-worn. He made no allusion to where he had been, although he was usually the frankest of men. It chanced, however, that our client here, Mr. Bennett, received a letter from a fellow-student in Prague, who said that he was glad to have seen Professor Presbury there, although he had not been able to talk to him. Only in this way did his own household learn where he had been.

"Now comes the point. From that time onwards a curious change came over the Professor. He became furtive and sly. Those around him had always the feeling that he was not the man that they had known, but that he was under some shadow which had darkened his higher qualities. His intellect was not affected. His lectures were as brilliant as ever. But always there was something new, something sinister and unexpected. His daughter, who was devoted to him, tried again and again to resume the old relations and to penetrate this mask which her father seemed to have put on. You, sir, as I understand, did the same—but all was in vain. And now, Mr. Bennett, tell in your own words the incident of the letters."

"You must understand, Dr. Watson, that the Professor had no secrets from me. If I were his son or his younger brother, I could not have more completely enjoyed his confidence. As his secretary I handled every paper which came to him, and I opened and subdivided his letters. Shortly after his return all this was changed. He told me that certain letters might come to him from London which would be marked by a cross under the stamp. These were to be set aside for his own eyes only. I may say that several of these did pass through my hands, that they had the E.C. mark, and were in an illiterate handwriting. If he answered them at all the answers did not pass through my hands nor into the letter-basket in which our correspondence was collected."

"And the box," said Holmes.

"Ah, yes, the box. The Professor brought back a little wooden box from his travels. It was the one thing which suggested a Continental tour, for it was one of those quaint carved things which one associates with Germany. This he placed in his instrument cupboard. One day, in looking for a cannula, I took up the box. To my surprise he was very angry, and reproved me in words which were quite savage for my curiosity. It was the first time such a thing had happened and I was deeply hurt. I endeavoured to explain that it was a mere accident that I had touched the box, but all the evening I was conscious that he looked at me harshly and that the incident was rankling in his mind." Mr. Bennett drew a little diary book from his pocket. "That was on July 2," said he.

"You are certainly an admirable witness," said Holmes. "I may need some of these dates which you have noted."

"I learned method among other things from my great teacher. From the time that I observed abnormality in his behaviour I felt that it was my duty to study his case. Thus I have it here that it was on that very day, July 2, that Roy attacked the Professor, as he came from his study into the hall. Again on July 11, there was a scene of the same sort and then I have a note of yet another upon July 20. After that we had to banish Roy to the stables. He was a dear, affectionate animal—but I fear I weary you."

Mr. Bennett spoke in a tone of reproach, for it was very clear that Holmes was not listening. His face was rigid and his eyes gazed abstractedly at the ceiling. With an effort he recovered himself.

"Singular! Most singular!" he murmured. "These details were new to me, Mr. Bennett. I think we have now fairly gone over the old ground, have we not? But you spoke of some fresh developments."

The pleasant, open face of our visitor clouded over, shadowed by some grim remembrance. "What I speak of occurred the night before last," said he. "I was lying awake about two in the morning, when I was aware of a dull muffled sound coming from the passage. I opened my door and peeped out. I should explain that the Professor sleeps at the end of the passage——"

"The date being——?" asked Holmes.

Our visitor was clearly annoyed at so irrelevant an interruption.

"I have said, sir, that it was the night before last—that is, September 4."

Holmes nodded and smiled.

"Pray continue," said he.

"He sleeps at the end of the passage, and would have to pass my door in order to reach the staircase. It was a really terrifying experience, Mr. Holmes. I think that I am as strong-nerved as my neighbours, but I was shaken by what I saw. The passage was dark save that one window half-way along it threw a patch of light. I could see that something was coming along the passage, something dark and crouching. Then suddenly it emerged into the light, and I saw that it was he. He was crawling, Mr. Holmes—crawling! He was not quite on his hands and knees. I should rather say on his hands and feet, with his face sunk between his hands. Yet he seemed to move with ease. I was so paralysed by the sight that it was not until he had reached my door that I was able to step forward and ask if I could assist him. His answer was extraordinary. He sprang up, spat out some atrocious word at me, and hurried on past me, and down the staircase. I waited about for an hour, but he did not come back. It must have been daylight before he regained his room."

"Well, Watson, what make you of that?" asked Holmes, with the air of the pathologist who presents a rare specimen.

"Lumbago, possibly. I have known a severe attack make a man walk in just such a way, and nothing would be more trying to the temper."

"Good, Watson! You always keep us flat-footed on the ground. But we can hardly accept lumbago, since he was able to stand erect in a moment."

"He was never better in health," said Bennett. "In fact, he is stronger than I have known him for years. But there are the facts, Mr. Holmes. It is not a case in which we can consult the police, and yet we are utterly at our wits' end as to what to do, and we feel in some strange way that we are drifting towards disaster. Edith—Miss Presbury—feels as I do, that we cannot wait passively any longer."

"It is certainly a very curious and suggestive case. What do you think, Watson?"

"Speaking as a medical man," said I, "it appears to be a case for an alienist. The old gentleman's cerebral processes were disturbed by the love affair. He made a journey abroad in the hope of breaking himself of the passion. His letters and the box may be connected with some other private transaction—a loan, perhaps, or share certificates, which are in the box."

"And the wolf-hound no doubt disapproved of the financial bargain. No, no, Watson, there is more in it than this. Now, I can only suggest——"

What Sherlock Holmes was about to suggest will never be known, for at this moment the door opened and a young lady was shown into the room. As she appeared Mr. Bennett sprang up with a cry and ran forward with his hands out to meet those which she had herself outstretched.

"Edith, dear! Nothing the matter, I hope?"

"I felt I must follow you. Oh, Jack, I have been so dreadfully frightened! It is awful to be there alone."

"Mr. Holmes, this is the young lady I spoke of. This is my fiancée."

"We were gradually coming to that conclusion, were we not, Watson?" Holmes answered, with a smile. "I take it, Miss Presbury, that there is some fresh development in the case, and that you thought we should know?"

Our new visitor, a bright, handsome girl of a conventional English type, smiled back at Holmes as she seated herself beside Mr. Bennett.

"When I found Mr. Bennett had left his hotel I thought I should probably find him here. Of course, he had told me that he would consult you. But, oh, Mr. Holmes, can you do nothing for my poor father?"

"I have hopes, Miss Presbury, but the case is still obscure. Perhaps what you have to say may throw some fresh light upon it."

"It was last night, Mr. Holmes. He had been very strange all day. I am sure that there are times when he has no recollection of what he does. He lives as in a strange dream. Yesterday was such a day. It was not my father with whom I lived. His outward shell was there, but it was not really he."

"Tell me what happened."

"I was awakened in the night by the dog barking most furiously. Poor Roy, he is chained now near the stable. I may say that I always sleep with my door locked; for, as Jack—as Mr. Bennett—will tell you, we all have a feeling of impending danger. My room is on the second floor. It happened that the blind was up in my window, and there was bright moonlight outside. As I lay with my eyes fixed upon the square of light, listening to the frenzied barkings of the dog, I was amazed to see my father's face looking in at me. Mr. Holmes, I nearly died of surprise and horror. There it was pressed against the window-pane, and one hand seemed to be raised as if to push up the window. If that window had opened, I think I should have gone mad. It was no delusion, Mr. Holmes. Don't deceive yourself by thinking so. I dare say it was twenty seconds or so that I lay paralysed and watched the face. Then it vanished, but I could not—I could not spring out of bed and look out after it. I lay cold and shivering till morning. At breakfast he was sharp and fierce in manner, and made no allusion to the adventure of the night. Neither did I, but I gave an excuse for coming to town—and here I am."

Holmes looked thoroughly surprised at Miss Presbury's narrative.

"My dear young lady, you say that your room is on the second floor. Is there a long ladder in the garden?"

"No, Mr. Holmes; that is the amazing part of it. There is no possible way of reaching the window—and yet he was there."

"The date being September 5," said Holmes. "That certainly complicates matters."

It was the young lady's turn to look surprised. "This is the second time that you have alluded to the date, Mr. Holmes," said Bennett. "Is it possible that it has any bearing upon the case?"

"It is possible—very possible—and yet I have not my full material at present."

"Possibly you are thinking of the connection between insanity and phases of the moon?"

"No, I assure you. It was quite a different line of thought. Possibly you can leave your notebook with me and I will check the dates. Now I think, Watson, that our line of action is perfectly clear. This young lady has informed us—and I have the greatest confidence in her intuition—that her father remembers little or nothing which occurs upon certain dates. We will therefore call upon him as if he had given us an appointment upon such a date. He will put it down to his own lack of memory. Thus we will open our campaign by having a good close view of him."

"That is excellent," said Mr. Bennett. "I warn you, however, that the Professor is irascible and violent at times."

Holmes smiled. "There are reasons why we should come at once—very cogent reasons if my theories hold good. To-morrow, Mr. Bennett, will certainly see us in Camford. There is, if I remember right, an inn called the 'Chequers' where the port used to be above mediocrity, and the linen was above reproach. I think, Watson, that our lot for the next few days might lie in less pleasant places."

Monday morning found us on our way to the famous University town—an easy effort on the part of Holmes, who had no roots to pull up, but one which involved frantic planning and hurrying on my part, as my practice was by this time not inconsiderable. Holmes made no allusion to the case until after we had deposited our suit-cases at the ancient hostel of which he had spoken.

"I think, Watson, that we can catch the Professor just before lunch. He lectures at eleven, and should have an interval at home."

"What possible excuse have we for calling?"

Holmes glanced at his notebook.

"There was a period of excitement upon August 26. We will assume that he is a little hazy as to what he does at such times. If we insist that we are there by appointment I think he will hardly venture to contradict us. Have you the effrontery necessary to put it through?"

"We can but try."

"Excellent, Watson! Compound of the Busy Bee and Excelsior. We can but try—the motto of the firm. A friendly native will surely guide us."

Such a one on the back of a smart hansom swept us past a row of ancient colleges, and finally turning into a tree-lined drive pulled up at the door of a charming house, girt round with lawns and covered with purple wistaria. Professor Presbury was certainly surrounded with every sign not only of comfort but of luxury. Even as we pulled up a grizzled head appeared at the front window, and we were aware of a pair of keen eyes from under shaggy brows which surveyed us through large horn glasses. A moment later we were actually in his sanctum, and the mysterious scientist, whose vagaries had brought us from London, was standing before us. There was certainly no sign of eccentricity either in his manner or appearance, for he was a portly, large-featured man, grave, tall, and frock-coated, with the dignity of bearing which a lecturer needs. His eyes were his most remarkable feature, keen, observant, and clever to the verge of cunning.

He looked at our cards. "Pray sit down, gentlemen. What can I do for you?"

Mr. Holmes smiled amiably.

"It was the question which I was about to put to you, Professor."

"To me, sir!"

"Possibly there is some mistake. I heard through a second person that Professor Presbury of Camford had need of my services."

"Oh, indeed!" It seemed to me that there was a malicious sparkle in the intense grey eyes. "You heard that, did you? May I ask the name of your informant?"

"I am sorry, Professor, but the matter was rather confidential. If I have made a mistake there is no harm done. I can only express my regret."

"Not at all. I should wish to go further into this matter. It interests me. Have you any scrap of writing, any letter or telegram, to bear out your assertion?"

"No, I have not."

"I presume that you do not go so far as to assert that I summoned you?"

"I would rather answer no questions," said Holmes.

"No, I dare say not," said the Professor, with asperity. "However, that particular one can be answered very easily without your aid."

He walked across the room to the bell. Our London friend, Mr. Bennett, answered the call.

"Come in, Mr. Bennett. These two gentlemen have come from London under the impression that they have been summoned. You handle all my correspondence. Have you a note of anything going to a person named Holmes?"

"No, sir," Bennett answered, with a flush.

"That is conclusive," said the Professor, glaring angrily at my companion. "Now, sir"—he leaned forward with his two hands upon the table—"it seems to me that your position is a very questionable one."

Holmes shrugged his shoulders.

"I can only repeat that I am sorry that we have made a needless intrusion."

"Hardly enough, Mr. Holmes!" the old man cried, in a high screaming voice, with extraordinary malignancy upon his face. He got between us and the door as he spoke, and he shook his two hands at us with furious passion. "You can hardly get out of it so easily as that." His face was convulsed and he grinned and gibbered at us in his senseless rage. I am convinced that we should have had to fight our way out of the room if Mr. Bennett had not intervened.

"My dear Professor," he cried, "consider your position! Consider the scandal at the University! Mr. Holmes is a well-known man. You cannot possibly treat him with such discourtesy."

Sulkily our host—if I may call him so—cleared the path to the door. We were glad to find ourselves outside the house, and in the quiet of the tree-lined drive. Holmes seemed greatly amused by the episode.

"Our learned friend's nerves are somewhat out of order," said he. "Perhaps our intrusion was a little crude, and yet we have gained that personal contact which I desired. But, dear me, Watson, he is surely at our heels. The villain still pursues us."

There were the sounds of running feet behind, but it was, to my relief, not the formidable Professor but his assistant who appeared round the curve of the drive. He came panting up to us.

"I am so sorry, Mr. Holmes. I wished to apologize."

"My dear sir, there is no need. It is all in the way of professional experience."

"I have never seen him in a more dangerous mood. But he grows more sinister. You can understand now why his daughter and I are alarmed. And yet his mind is perfectly clear."

"Too clear!" said Holmes. "That was my miscalculation. It is evident that his memory is much more reliable than I had thought. By the way, can we, before we go, see the window of Miss Presbury's room?"

Mr. Bennett pushed his way through some shrubs and we had a view of the side of the house.

"It is there. The second on the left."

"Dear me, it seems hardly accessible. And yet you will observe that there is a creeper below and a water-pipe above which give some foothold."

"I could not climb it myself," said Mr. Bennett.

"Very likely. It would certainly be a dangerous exploit for any normal man."

"There was one other thing I wished to tell you, Mr. Holmes. I have the address of the man in London to whom the Professor writes. He seems to have written this morning and I got it from his blotting-paper. It is an ignoble position for a trusted secretary, but what else can I do?"

Holmes glanced at the paper and put it into his pocket.

"Dorak—a curious name. Slavonic, I imagine. Well, it is an important link in the chain. We return to London this afternoon, Mr. Bennett. I see no good purpose to be served by our remaining. We cannot arrest the Professor, because he has done no crime, nor can we place him under constraint, for he cannot be proved to be mad. No action is as yet possible."

"Then what on earth are we to do?"

"A little patience, Mr. Bennett. Things will soon develop. Unless I am mistaken next Tuesday may mark a crisis. Certainly we shall be in Camford on that day. Meanwhile, the general position is undeniably unpleasant, and if Miss Presbury can prolong her visit——"

"That is easy."

"Then let her stay till we can assure her that all danger is past. Meanwhile, let him have his way and do not cross him. So long as he is in a good humour all is well."

"There he is!" said Bennett, in a startled whisper. Looking between the branches we saw the tall, erect figure emerge from the hall door and look around him. He stood leaning forward, his hands swinging straight before him, his head turning from side to side. The secretary with a last wave slipped off among the trees, and we saw him presently rejoin his employer, the two entering the house together in what seemed to be animated and even excited conversation.

"I expect the old gentleman has been putting two and two together," said Holmes, as we walked hotelwards. "He struck me as having a particularly clear and logical brain, from the little I saw of him. Explosive, no doubt, but then from his point of view he has something to explode about if detectives are put on his track and he suspects his own household of doing it. I rather fancy that friend Bennett is in for an uncomfortable time."

Holmes stopped at a post office and sent off a telegram on our way. The answer reached us in the evening, and he tossed it across to me. "Have visited the Commercial Road and seen Dorak. Suave person, Bohemian, elderly. Keeps large general store.—Mercer."

"Mercer is since your time," said Holmes. "He is my general utility man who looks up routine business. It was important to know something of the man with whom our Professor was so secretly corresponding. His nationality connects up with the Prague visit."

"Thank goodness that something connects with something," said I. "At present we seem to be faced by a long series of inexplicable incidents with no bearing upon each other. For example, what possible connection can there be between an angry wolf-hound and a visit to Bohemia, or either of them with a man crawling down a passage at night? As to your dates, that is the biggest mystification of all."

Holmes smiled and rubbed his hands. We were, I may say, seated in the old sitting-room of the ancient hotel, with a bottle of the famous vintage of which Holmes had spoken on the table between us.

"Well, now, let us take the dates first," said he, his finger-tips together and his manner as if he were addressing a class. "This excellent young man's diary shows that there was trouble upon July 2, and from then onwards it seems to have been at nine-day intervals, with, so far as I remember, only one exception. Thus the last outbreak upon Friday was on September 3, which also falls into the series, as did August 26, which preceded it. The thing is beyond coincidence."

I was forced to agree.

"Let us, then, form the provisional theory that every nine days the Professor takes some strong drug which has a passing but highly poisonous effect. His naturally violent nature is intensified by it. He learned to take this drug while he was in Prague, and is now supplied with it by a Bohemian intermediary in London. This all hangs together, Watson!"

"But the dog, the face at the window, the creeping man in the passage?"

"Well, well, we have made a beginning. I should not expect any fresh developments until next Tuesday. In the meantime we can only keep in touch with friend Bennett and enjoy the amenities of this charming town."

In the morning Mr. Bennett slipped round to bring us the latest report. As Holmes had imagined, times had not been easy with him. Without exactly accusing him of being responsible for our presence, the Professor had been very rough and rude in his speech, and evidently felt some strong grievance. This morning he was quite himself again, however, and had delivered his usual brilliant lecture to a crowded class. "Apart from his queer fits," said Bennett, "he has actually more energy and vitality than I can ever remember, nor was his brain ever clearer. But it's not he—it's never the man whom we have known."

"I don't think you have anything to fear now for a week at least," Holmes answered. "I am a busy man, and Dr. Watson has his patients to attend to. Let us agree that we meet here at this hour next Tuesday, and I shall be surprised if before we leave you again we are not able to explain, even if we cannot perhaps put an end to, your troubles. Meanwhile, keep us posted in what occurs."

I saw nothing of my friend for the next few days, but on the following Monday evening I had a short note asking me to meet him next day at the train. From what he told me as we travelled up to Camford all was well, the peace of the Professor's house had been unruffled, and his own conduct perfectly normal. This also was the report which was given us by Mr. Bennett himself when he called upon us that evening at our old quarters in the "Chequers." "He heard from his London correspondent to-day. There was a letter and there was a small packet, each with the cross under the stamp which warned me not to touch them. There has been nothing else."

"That may prove quite enough," said Holmes grimly. "Now, Mr. Bennett, we shall, I think, come to some conclusion to-night. If my deductions are correct we should have an opportunity of bringing matters to a head. In order to do so it is necessary to hold the Professor under observation. I would suggest, therefore, that you remain awake and on the look out. Should you hear him pass your door do not interrupt him, but follow him as discreetly as you can. Dr. Watson and I will not be far off. By the way, where is the key of that little box of which you spoke?"

"Upon his watch-chain."

"I fancy our researches must lie in that direction. At the worst the lock should not be very formidable. Have you any other able-bodied man on the premises?"

"There is the coachman, Macphail."

"Where does he sleep?"

"Over the stables."

"We might possibly want him. Well, we can do no more until we see how things develop. Good-bye—but I expect that we shall see you before morning."

It was nearly midnight before we took our station among some bushes immediately opposite the hall door of the Professor. It was a fine night, but chilly, and we were glad of our warm overcoats. There was a breeze, and clouds were scudding across the sky, obscuring from time to time the half-moon. It would have been a dismal vigil were it not for the expectation and excitement which carried us along, and the assurance of my comrade that we had probably reached the end of the strange sequence of events which had engaged our attention.

"If the cycle of nine days holds good then we shall have the Professor at his worst to-night," said Holmes. "The fact that these strange symptoms began after his visit to Prague, that he is in secret correspondence with a Bohemian dealer in London, who presumably represents someone in Prague, and that he received a packet from him this very day, all point in one direction. What he takes and why he takes it are still beyond our ken, but that it emanates in some way from Prague is clear enough. He takes it under definite directions which regulate this ninth-day system, which was the first point which attracted my attention. But his symptoms are most remarkable. Did you observe his knuckles?"

I had to confess that I did not.

"Thick and horny in a way which is quite new in my experience. Always look at the hands first, Watson. Then cuffs, trouser-knees, and boots. Very curious knuckles which can only be explained by the mode of progression observed by——" Holmes paused, and suddenly clapped his hand to his forehead. "Oh, Watson, Watson, what a fool I have been! It seems incredible, and yet it must be true. All points in one direction. How could I miss seeing the connection of ideas? Those knuckles—how could I have passed those knuckles? And the dog! And the ivy! It's surely time that I disappeared into that little farm of my dreams. Look out, Watson! Here he is! We shall have the chance of seeing for ourselves."

The hall door had slowly opened, and against the lamp-lit background we saw the tall figure of Professor Presbury. He was clad in his dressing-gown. As he stood outlined in the doorway he was erect but leaning forward with dangling arms, as when we saw him last.

Now he stepped forward into the drive, and an extraordinary change came over him. He sank down into a crouching position, and moved along upon his hands and feet, skipping every now and then as if he were overflowing with energy and vitality. He moved along the face of the house and then round the corner. As he disappeared Bennett slipped through the hall door and softly followed him.

"Come, Watson, come!" cried Holmes, and we stole as softly as we could through the bushes until we had gained a spot whence we could see the other side of the house, which was bathed in the light of the half-moon. The Professor was clearly visible crouching at the foot of the ivy-covered wall. As we watched him he suddenly began with incredible agility to ascend it. From branch to branch he sprang, sure of foot and firm of grasp, climbing apparently in mere joy at his own powers, with no definite object in view. With his dressing-gown flapping on each side of him he looked like some huge bat glued against the side of his own house, a great square dark patch upon the moonlit wall. Presently he tired of this amusement, and, dropping from branch to branch, he squatted down into the old attitude and moved towards the stables, creeping along in the same strange way as before. The wolf-hound was out now, barking furiously, and more excited than ever when it actually caught sight of its master. It was straining on its chain, and quivering with eagerness and rage. The Professor squatted down very deliberately just out of reach of the hound, and began to provoke it in every possible way. He took handfuls of pebbles from the drive and threw them in the dog's face, prodded him with a stick which he had picked up, flicked his hands about only a few inches from the gaping mouth, and endeavoured in every way to increase the animal's fury, which was already beyond all control. In all our adventures I do not know that I have ever seen a more strange sight than this impassive and still dignified figure crouching frog-like upon the ground and goading to a wilder exhibition of passion the maddened hound, which ramped and raged in front of him, by all manner of ingenious and calculated cruelty.

And then in a moment it happened! It was not the chain that broke, but it was the collar that slipped, for it had been made for a thick-necked Newfoundland. We heard the rattle of falling metal, and the next instant dog and man were rolling on the ground together, the one roaring in rage, the other screaming in a strange shrill falsetto of terror. It was a very narrow thing for the Professor's life. The savage creature had him fairly by the throat, its fangs had bitten deep, and he was senseless before we could reach them and drag the two apart. It might have been a dangerous task for us, but Bennett's voice and presence brought the great wolf-hound instantly to reason. The uproar had brought the sleepy and astonished coachman from his room above the stables. "I'm not surprised," said he, shaking his head. "I've seen him at it before. I knew the dog would get him sooner or later."

The hound was secured, and together we carried the Professor up to his room, where Bennett, who had a medical degree, helped me to dress his torn throat. The sharp teeth had passed dangerously near the carotid artery, and the hemorrhage was serious. In half an hour the danger was past, I had given the patient an injection of morphia, and he had sunk into deep sleep. Then, and only then, were we able to look at each other and to take stock of the situation.

"I think a first-class surgeon should see him," said I.

"For God's sake, no!" cried Bennett. "At present the scandal is confined to our own household. It is safe with us. If it gets beyond these walls it will never stop. Consider his position at the University, his European reputation, the feelings of his daughter."

"Quite so," said Holmes. "I think it may be quite possible to keep the matter to ourselves, and also to prevent its recurrence now that we have a free hand. The key from the watch-chain, Mr. Bennett. Macphail will guard the patient and let us know if there is any change. Let us see what we can find in the Professor's mysterious box."

There was not much, but there was enough—an empty phial, another nearly full, a hypodermic syringe, several letters in a crabbed, foreign hand. The marks on the envelopes showed that they were those which had disturbed the routine of the secretary, and each was dated from the Commercial Road and signed "A. Dorak." They were mere invoices to say that a fresh bottle was being sent to Professor Presbury, or receipts to acknowledge money. There was one other envelope, however, in a more educated hand and bearing the Austrian stamp with the postmark of Prague. "Here we have our material!" cried Holmes, as he tore out the enclosure.

"HONOURED COLLEAGUE," it ran. "Since your esteemed visit I have thought much of your case, and though in your circumstances there are some special reasons for the treatment, I would none the less enjoin caution, as my results have shown that it is not without danger of a kind.

"It is possible that the Serum of Anthropoid would have been better. I have, as I explained to you, used black-faced Langur because a specimen was accessible. Langur is, of course, a crawler and climber, while Anthropoid walks erect, and is in all ways nearer.

"I beg you to take every possible precaution that there be no premature revelation of the process. I have one other client in England, and Dorak is my agent for both.

"Weekly reports will oblige.

"Yours with high esteem,
"H. LOWENSTEIN."

Lowenstein! The name brought back to me the memory of some snippet from a newspaper which spoke of an obscure scientist who was striving in some unknown way for the secret of rejuvenescence and the elixir of life. Lowenstein of Prague! Lowenstein with the wondrous strength-giving serum, tabooed by the profession because he refused to reveal its source. In a few words I said what I remembered. Bennett had taken a manual of Zoology from the shelves. "'Langur,'" he read, "'the great black-faced monkey of the Himalayan slopes, biggest and most human of climbing monkeys.' Many details are added. Well, thanks to you, Mr. Holmes, it is very clear that we have traced the evil to its source."

"The real source," said Holmes, "lies, of course, in that untimely love affair which gave our impetuous Professor the idea that he could only gain his wish by turning himself into a younger man. When one tries to rise above Nature one is liable to fall below it. The highest type of man may revert to the animal if he leaves the straight road of destiny." He sat musing for a little with the phial in his hand, looking at the clear liquid within. "When I have written to this man and told him that I hold him criminally responsible for the poisons which he circulates, we will have no more trouble. But it may recur. Others may find a better way. There is danger there—a very real danger to humanity. Consider, Watson, that the material, the sensual, the worldly would all prolong their worthless lives. The spiritual would not avoid the call to something higher. It would be the survival of the least fit. What sort of cesspool may not our poor world become?" Suddenly the dreamer disappeared, and Holmes, the man of action, sprang from his chair. "I think there is nothing more to be said, Mr. Bennett. The various incidents will now fit themselves easily into the general scheme. The dog, of course, was aware of the change far more quickly than you. His smell would ensure that. It was the monkey, not the Professor, whom Roy attacked, just as it was the monkey who teased Roy. Climbing was a joy to the creature, and it was a mere chance, I take it, that the pastime brought him to the young lady's window. There is an early train to town, Watson, but I think we shall just have time for a cup of tea at the 'Chequers' before we catch it."

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