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 26th. 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 gray 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 wish 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 hotelward. 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 wolfhound 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 fingertips together and his manner as if he were addressing a class. This excellent young man’s diary shows that there was trouble upon July 2d, and from then onward 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 3d, which also falls into the series, as did August 26th, 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 tonight. 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 lookout. 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 lamplit 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 wolfhound 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 haemorrhage 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 receipt 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 insure 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.