One would not have regarded it as a thrilling occupation. Indeed there was rather a suggestion of monotony in the endless recurrence of examination, comparison, and measurements of things which appeared to be merely mechanical repetitions of one another. Nor did the brief and scanty jottings in the “notes” column suggest that this tedious procedure was yielding any great wealth of information. Nevertheless, Thorndyke continued to work at his task methodically, attentively, and without any symptoms of boredom, until he had dealt with nearly half of the strip. But at this point his manner underwent a sudden and remarkable change. Hitherto he had carried on his work with the placid air of one who is engaged on a mildly interesting piece of routine work. Now he sat up stiffly, gazing at the strip of photographs before him with a frown of perplexity, even of incredulity. With intense attention, he re-examined the last half-dozen prints that he had dealt with; then, taking a right foot as a starting-point, he followed the strip rapidly, taking no measurements and making no notes, until he reached the end, where he found a slip of paper pasted to the strip and bearing the note: “Footprints cease here. Track turned off to left into heather. Length of foot, 121/2 inches. Length of stride from heel to heel, 34 inches.”

  Having rapidly copied this note on to his block, Thorndyke resumed his examination with eager interest. Returning to the starting-point, he again examined a print of the left foot and then followed its successive prints to the final one at the end of the strip. Again he came back to the starting-point; but now, taking this as a centre, he began to move backwards and forwards, at first taking a dozen prints in each direction, then, by degrees, reducing the distance of his excursions until he came down to a single print of the right foot – a specially clear impression, marked with the number 93. This he again examined through the little microscope with the most intense scrutiny. Then, with a like concentrated attention, he examined first the preceding right-foot print, 91, and then the succeeding one, 95. Finally, he turned to the map to locate number 93, which he found near the middle of a wall – apparently the enclosing wall of a large garden or plantation – and exactly opposite a gate in that wall.

  From this moment Thorndyke’s interest in his original investigations seemed to become extinct. The little microscope, the scale, even the photographs themselves, were neglected and unnoticed, while he sat with his eyes fixed on the map – yet seeming to look through it rather than at it – evidently immersed in profound thought. For a long time he sat thus, immovable as a seated statue. At length he rose from his chair, and, mechanically filling his pipe, began slowly to pace up and down the room, and to any observer who knew him, had there been one, the intense gravity of his expression, the slight frown, the compressed lips, the downcast eyes, as well as the unlighted pipe that he grasped in his hand, would have testified that some problem of more than common intricacy was being turned over in his mind and its factors sorted out and collated.

  He had been pacing the room for nearly half an hour when a key was softly inserted into the latch of the outer door. The door opened and closed quietly, and then a gentle tap on the knocker of the inner door heralded the entry of a small gentleman of somewhat clerical aspect and uncommon crinkliness of countenance, who greeted Thorndyke with a deprecating smile.

  “I hope, sir,” said he, “that I am not disturbing you, but I thought that I had better remind you that you have not had any supper.”

  “Dear me!” exclaimed Thorndyke. “What a memory you have, Polton. And to think that I, who am really the interested party, should have overlooked the fact. Well, what do you propose?”

  Polton glanced at the table with a sympathetic eye. “You won’t want your things disturbed, I expect, if you have got a job on hand. I had better put your supper in the little laboratory. It won’t take more than five minutes.”

  “That will do admirably,” said Thorndyke. “And, by the way, I think that adjourned inquest at Aylesbury is the day after tomorrow, isn’t it?”

  “Yes, sir, Thursday. I fixed the letter on the appointment board.”

  “Well, as there is nothing pressing on Friday, I think I will stay the night there and come back on Friday evening if nothing urgent turns up in the interval.”

  “Yes, sir. Will you want anything special in the research case?”

  “I shall not take the research case,” replied Thorndyke; “in fact, I don’t know that I want anything excepting the one-inch ordnance map, unless I take that stick of yours.”

  Polton’s face brightened. “I wish you would, sir,” he said persuasively. “You have never tried it since I made it, and I am sure you will find it a most useful instrument.”

  “I am sure I shall,” said Thorndyke; “and perhaps I might as well take the little telephoto camera, if you will have it charged.”

  “I will charge it tonight, sir, and overhaul the stick. And your supper will be ready in five minutes.”

  With this Polton disappeared silently as he had come, leaving his principal to his meditations.

  On the following Friday morning, at about half-past ten, Dr John Thorndyke might have been seen – if there had been anyone to see him, which there was not – seated in a first-class smoking-compartment in the Aylesbury to London train. But he was evidently not going to London, for, as the train slowed down on approaching Borley station, he pocketed the folded ordnance map which he had been studying, stood up and took his stick down from the rack.

  Now this stick was the only blot on Thorndyke’s appearance. Apart from it his “turn-out” was entirely satisfactory and appropriate to his country surroundings without being either rustic or sporting. But that stick, with a tweed suit and a soft hat, struck a note of deepest discord. With a frock-coat and a top-hat it might have passed, though even then it would have called for a Falstaffian bearer. But as a country stick it really wouldn’t do at all.

  In the first place it was offensively straight – as straight as a length of metal tube. It was of an uncomely thickness, a full inch in diameter. As to the material, it might, by an exceedingly bad judge, have been mistaken for ebony. In fact, it was, as to its surface, strongly reminiscent of optician’s black enamel. And the handle was no better. Of the same funereal hue and an unreasonable thickness, it had the stark mechanical regularity of an elbow-joint on a gas pipe, and, to make it worse, its end was finished by a sort of terminal cap. Moreover, on looking down the shaft of the stick, a close observer would have detected, about fifteen inches from the handle, a fine transverse crack, suggestive of a concealed joint. A sharp-eyed rural constable would have “spotted” it at a glance as a walking-stick gun; and he would have been wrong.

  However, despite its aesthetic shortcomings, Thorndyke seemed to set some store by it, for he lifted it from the rack with evident care, and with the manner of lifting something heavier than an ordinary walking-stick; and when he stepped forth from the station, instead of holding it by its unlovely handle with its ferrule on the ground, he carried it “at the trail,” grasping it by its middle.

  On leaving the station precincts, Thorndyke set forth with the confident air of one who is on familiar ground, though, as a matter of fact, he had never been in the district before; but he had that power, which comes by practice, of memorizing a map that makes unvisited regions familiar and is apt to cause astonishment to the aboriginal inhabitants. Swinging along at an easy but rapid pace, he presently entered a quiet, semi-suburban road which he followed for a quarter of a mile, looking about him keenly, and identifying the features of the map as he went. At length he came to a kissing-gate which gave access to a footpath, and, turning into this, he strode away along the path, looking closely at its surface and once stopping and retracing his steps for a few yards to examine his own footprints.

  A few hundred yards farther on he crossed another road, more definitely rural in character, and noted at the corner a pleasant-looking house of some age, standing back behind a well-kept garden, its front entrance sheltered by a wooden porch which was now almost hidden by a mass of climbing roses. The side wall of the garden abutted on the footpath and extended along it for a distance that suggested somewhat extensive grounds. At this point Thorndyke reduced his pace to a slow walk, scrutinizing the ground – on which he could detect, even now, occasional fragmentary traces of the familiar footprints of Harold’s photographs – and noting how, since crossing the road, he had passed completely out of the last vestiges of the town into the open country.

  He had traversed rather more than half the length of the wall when he came to a green-painted wooden gate, before which he halted for a few moments. There were, however, no features of interest to note beyond the facts that its loop handle was unprovided with a latch and that it was secured with a Yale lock. But as he stood looking at it with a deeply reflective air, he was aware of a sound proceeding from within – a pleasant sound, though curiously out of key with his own thoughts – the sound of someone whistling, very skilfully and melodiously, the old-fashioned air, “Alice, where art thou?” He smiled grimly, keenly appreciative of the whimsical incongruity of these cheerful, innocent strains with the circumstances that had brought him thither; then he turned away and walked slowly to the end of the wall where it was joined by another, which enclosed the end of the grounds. Here he halted and looked along the path towards a wood which was visible in the distance; then, turning, he looked back along the way by which he had come. In neither direction was there anyone in sight, and Thorndyke noted that he had not met a single person since he had passed through the kissing-gate. Apparently this path was quite extraordinarily unfrequented.

  Having made this observation, Thorndyke stepped off the path and walked a few paces along the end wall – which abutted on a field – to a spot where an apple tree in the grounds rose above the summit. Here he stopped, and, having glanced up at the wall – which was nearly seven feet high – grasped the uncomely stick with both hands, one on either side of the concealed joint, and gave a sharp twist. Immediately the stick became divided into two parts, the lower of which – that bearing the ferrule – Thorndyke stood against the wall. It could now be seen that the upper part terminated in a blackened brass half-cylinder, the flat face of which was occupied by a little circular glass window, and when Thorndyke had unscrewed the cap from the end of the handle, the latter was seen to be a metal tube, within which was another little glass window – the eye-piece. In effect, Polton’s hideous walking-stick was a disguised periscope.

  Taking up a position close to the wall, Thorndyke slowly raised the periscope until its end stood an inch or so above the top of the wall, with the little window looking into the enclosure. The eye-piece being now at a convenient level, he applied his eye to it, and immediately had the sensation of looking through a circular hole in the wall. Through this aperture (which was, of course, the aperture of the object-glass above him, reflected by a pair of prisms) he looked into a large garden, enclosed on all sides by the high wall and having apparently only two doors or gates, the one at the side, which he had already seen, and another which appeared to open into another garden nearer the house, and which, like the side gate, seemed to be fitted with a night-latch of the Yale type. On one side, partly concealed by a half-grown yew hedge, was a long, low building which, by the windows in its roof, appeared to be some kind of workshop; and by rotating the periscope it was possible to catch a glimpse of part of what seemed to be a summer-house in the corner opposite the workshop. Otherwise, excepting a narrow flower border and a few fruit trees ranged along the wall, the whole of the enclosure was occupied by a large lawn, the wide expanse of which was broken only by a sundial, beside which, at the moment, a man was standing; and on man and sundial, Thorndyke, after his swift preliminary survey, concentrated his attention.

  The stone pillar of the dial was obviously ancient. Equally obviously the stone base on which it stood was brand new. Moreover, the part of the lawn immediately surrounding the base was yellow and faded as if it had been recently raised and relaid. The manifest inference was that the dial had but lately been placed in its present position; and this inference was supported by the occupation in which the man was engaged. On the stone base stood a Windsor chair, the seat of which bore one or two tools and a pair of spectacles. Thorndyke noted the spectacles with interest, observing that they had “curl sides” and were therefore habitually worn; and since they had been discarded while their owner consulted a book that he held, it seemed to follow that he must be near-sighted.

  As Thorndyke watched, the man closed the book and laid it on the chair, when by its shape and size, its scarlet back and apple-green sides, it was easily recognizable as Whitaker’s Almanack. Having laid down the book, the man drew out his watch, and, holding it in his hand, approached the pillar and grasped the gnomon of the dial; and now Thorndyke could see that the dial-plate had been unfixed from its bed, for it moved visibly as the gnomon was grasped. The nature of the operation was now quite clear. The man was re-setting the dial. He had taken out the Equation of Time from Whitaker and was now adjusting the dial-plate by means of his watch to show the correct Apparent Solar Time.

  At this point – leaving the man standing beside the pillar, watch in hand – Thorndyke picked up the detached portion of the stick, and stepping along the wall, glanced up and down the path. So far as he could see – nearly a quarter of a mile in each direction – he had the path to himself; and, noting with some surprise and no little interest the remarkable paucity of wayfarers, he returned to his post and resumed his observations.

  The man had now put away his watch and taken up a hammer and bradawl. Thorndyke noted the workmanlike character of the former – a rather heavy ball-pane hammer such as engineers use – and when the bradawl was inserted into one of the screw-holes of the dial-plate and driven home into the lead bed with a single tap, he observed the deftness with which the gentle, calculated blow was delivered with the rather ponderous tool. So, too, with the driving of the screw; it was done with the unmistakable ease and readiness of the skilled workman.

  Having rapidly made these observations, Thorndyke drew from his hip pocket the little camera and opened it, setting the focus by the scale to the assumed distance – about sixty feet – fixing the wire release and setting the shutter to half a second – the shortest exposure that was advisable with a telephoto lens. Another peep through the periscope showed the man in the act of again inserting the bradawl, and, incidentally, presenting a well-lighted right profile; whereupon Thorndyke raised the camera and placed it on the top of the wall with the wire release hanging down and the lens pointed, as well as he could judge, at the sundial. Then, as the man poised the hammer preparatory to striking, he pressed the button of the release and immediately took down the camera and changed the film.

  Once more he went to the corner of the wall and looked up and down the path. This time a man was visible – apparently a labourer – coming from the direction of the town. But he was a long distance away and was advancing at a pace so leisurely that Thorndyke decided to complete his business, if possible, before he should arrive. A glance through the periscope showed the man in the garden driving another screw. When he had driven it home, he stepped round the pillar to deal with the screws on the other side. As he inserted the bradawl and balanced the hammer, presenting now his left profile, Thorndyke lifted the camera to the top of the wall, made the exposure, took down the camera, and having changed the film, closed it and put it in his pocket. Then he joined up the two parts of the stick, fixed the cap on the eye-piece and came out on to the path, turning towards the town to meet the labourer. But the latter had now disappeared, having apparently turned into the road on which the house fronted. Having the path once more to himself, Thorndyke walked along it to the gate, where he paused and rapped on it smartly with his knuckles.

  After a short interval, during which he repeated the summons, the gate was opened a few inches and the man whom he had seen within looked out with an air of slightly irritable enquiry.

  “I must apologize for disturbing you,” Thorndyke said with disarming suavity, “but I heard someone within, and there was no one about from whom I could make my enquiry.”

  “You are not disturbing me in the least,” the other replied, not less suavely. “I shall be most happy to give you any information that I can. What was the enquiry that you wished to make?”

  As he asked the question, the stranger stepped out on the path, drawing the gate to after him, and looked inquisitively at Thorndyke.

  “I wanted to know,” the latter replied, “whether this footpath leads to a wood – Potter’s Wood, I think it is called. You see, I am a stranger to this neighbourhood.”

  On this the man seemed to look at him with heightened interest as he replied:

  “Yes, it leads through the wood about half a mile farther on.”

  “And where does it lead to eventually?”

  “It crosses a patch of heath and joins a by-road that runs from the town to the main London road. Was that where you wanted to go?”

  “No,” replied Thorndyke. “It is the path itself that I am concerned with. The fact is, I am making a sort of informal inspection in connection with the case of a man who disappeared a short time ago – the manager of a local branch of Perkins’s Bank. I understand that he was last seen walking along this path.”