The omnibus of those days was a leisurely vehicle. Its ordinary pace was a rather sluggish trot, and in a thickly populated thoroughfare its speed was further reduced by frequent stoppages. Bearing these facts in mind, I gave an occasional backward glance as we jogged northward, though my attention soon began to wander from the rather remote possibility of pursuit to the incidents of our late exploration.
 
It had not been difficult to see that Thorndyke was very well pleased with the results of our search, but excepting the letter—which undoubtedly opened up a channel for further inquiry and possible identification—I could not perceive that any of the traces that we had found justified his satisfaction. There were the spectacles, for instance. They were almost certainly the pair worn by Mr. Graves. But what then? It was exceedingly improbable that we should be able to discover the maker of them, and if we were, it was still more improbable that he would be able to give us any information that would help us. Spectacle-makers are not usually on confidential terms with their customers.
 
As to the other objects, I could make nothing of them. The little sticks of reed evidently had some use that was known to Thorndyke and furnished, by inference, some kind of information about Weiss, Graves, or Mrs. Schallibaum. But I had never seen anything like them before and they conveyed nothing whatever to me. Then the bottle that had seemed so significant to Thorndyke was to me quite uninforming. It did, indeed, suggest that some member of the household might be connected with the stage, but it gave no hint as to which one. Certainly that person was not Mr. Weiss, whose appearance was as remote from that of an actor as could well be imagined. At any rate, the bottle and its label gave me no more useful hint than it might be worth while to call on Mr. Fox and make inquiries; and something told me very emphatically that this was not what it had conveyed to Thorndyke.
 
These reflections occupied me until the omnibus, having rumbled over London Bridge and up King William Street, joined the converging streams of traffic at the Mansion House. Here I got down and changed to an omnibus bound for Kensington; on which I travelled westward pleasantly enough, looking down into the teeming streets and whiling away the time by meditating upon the very agreeable afternoon that I promised myself, and considering how far my new arrangement with Thorndyke would justify me in entering into certain domestic engagements of a highly interesting kind.
 
What might have happened under other circumstances it is impossible to tell and useless to speculate; the fact is that my journey ended in a disappointment. I arrived, all agog, at the familiar house in Endsley Gardens only to be told by a sympathetic housemaid that the family was out; that Mrs. Hornby had gone into the country and would not be home until night, and—which mattered a good deal more to me—that her niece, Miss Juliet Gibson, had accompanied her.
 
Now a man who drops into lunch without announcing his intention or previously ascertaining those of his friends has no right to quarrel with fate if he finds an empty house. Thus philosophically I reflected as I turned away from the house in profound discontent, demanding of the universe in general why Mrs. Hornby need have perversely chosen my first free day to go gadding into the country, and above all, why she must needs spirit away the fair Juliet. This was the crowning misfortune (for I could have endured the absence of the elder lady with commendable fortitude), and since I could not immediately return to the Temple it left me a mere waif and stray for the time being.
 
Instinct—of the kind that manifests itself especially about one o'clock in the afternoon—impelled me in the direction of Brompton Road, and finally landed me at a table in a large restaurant apparently adjusted to the needs of ladies who had come from a distance to engage in the feminine sport of shopping. Here, while waiting for my lunch, I sat idly scanning the morning paper and wondering what I should do with the rest of the day; and presently it chanced that my eye caught the announcement of a matinée at the theatre in Sloane Square. It was quite a long time since I had been at a theatre, and, as the play—light comedy—seemed likely to satisfy my not very critical taste, I decided to devote the afternoon to reviving my acquaintance with the drama. Accordingly as soon as my lunch was finished, I walked down the Brompton Road, stepped on to an omnibus, and was duly deposited at the door of the theatre. A couple of minutes later I found myself occupying an excellent seat in the second row of the pit, oblivious alike of my recent disappointment and of Thorndyke's words of warning.
 
I am not an enthusiastic play-goer. To dramatic performances I am disposed to assign nothing further than the modest function of furnishing entertainment. I do not go to a theatre to be instructed or to have my moral outlook elevated. But, by way of compensation, I am not difficult to please. To a simple play, adjusted to my primitive taste, I can bring a certain bucolic appreciation that enables me to extract from the performance the maximum of enjoyment; and when, on this occasion, the final curtain fell and the audience rose, I rescued my hat from its insecure resting-place and turned to go with the feeling that I had spent a highly agreeable afternoon.
 
Emerging from the theatre, borne on the outgoing stream, I presently found myself opposite the door of a tea-shop. Instinct—the five o'clock instinct this time—guided me in; for we are creatures of habit, especially of the tea habit. The unoccupied table to which I drifted was in a shady corner not very far from the pay-desk; and here I had been seated less than a minute when a lady passed me on her way to the farther table. The glimpse that I caught of her as she approached—it was but a glimpse, since she passed behind me—showed that she was dressed in black, that she wore a beaded veil and hat, and in addition to the glass of milk and the bun that she carried, she was encumbered by an umbrella and a small basket, apparently containing some kind of needlework. I must confess that I gave her very little attention at the time, being occupied in anxious speculation as to how long it would be before the fact of my presence would impinge on the consciousness of the waitress.
 
The exact time by the clock on the wall was three minutes and a quarter, at the expiration of which an anaemic young woman sauntered up to the table and bestowed on me a glance of sullen interrogation, as if mutely demanding what the devil I wanted. I humbly requested that I might be provided with a pot of tea; whereupon she turned on her heel (which was a good deal worn down on the offside) and reported my conduct to a lady behind a marble-topped counter.
 
It seemed that the counter lady took a lenient view of the case, for in less than four minutes the waitress returned and gloomily deposited on the table before me a tea-pot, a milk-jug, a cup and saucer, a jug of hot water, and a small pool of milk. Then she once more departed in dudgeon.
 
I had just given the tea in the pot a preliminary stir and was about to pour out the first cup when I felt some one bump lightly against my chair and heard something rattle on the floor. I turned quickly and perceived the lady, whom I had seen enter, stooping just behind my chair. It seemed that having finished her frugal meal she was on her way out when she had dropped the little basket that I had noticed hanging from her wrist; which basket had promptly disgorged its entire contents on the floor.
 
Now every one must have noticed the demon of agility that seems to enter into an inanimate object when it is dropped, and the apparently intelligent malice with which it discovers, and rolls into, the most inaccessible places. Here was a case in point. This particular basket had contained materials for Oriental bead-work; and no sooner had it reached the floor than each item of its contents appeared to become possessed of a separate and particular devil impelling it to travel at headlong speed to some remote and unapproachable corner as distant as possible from its fellows.
 
As the only man—and almost the only person—near, the duty of salvage-agent manifestly devolved upon me; and down I went, accordingly, on my hands and knees, regardless of a nearly new pair of trousers, to grope under tables, chairs and settles in reach of the scattered treasure. A ball of the thick thread or twine I recovered from a dark and dirty corner after a brief interview with the sharp corner of a settle, and a multitude of the large beads with which this infernal industry is carried on I gathered from all parts of the compass, coming forth at length (quadrupedally) with a double handful of the treasure-trove and a very lively appreciation of the resistant qualities of a cast-iron table-stand when applied to the human cranium.
 
The owner of the lost and found property was greatly distressed by the accident and the trouble it had caused me; in fact she was quite needlessly agitated about it. The hand which held the basket into which I poured the rescued trash trembled visibly, and the brief glance that I bestowed on her as she murmured her thanks and apologies—with a very slight foreign accent—showed me that she was excessively pale. That much I could see plainly in spite of the rather dim light in this part of the shop and the beaded veil that covered her face; and I could also see that she was a rather remarkable looking woman, with a great mass of harsh, black hair and very broad black eyebrows that nearly met above her nose and contrasted strikingly with the dead white of her skin. But, of course, I did not look at her intently. Having returned her property and received her acknowledgments, I resumed my seat and left her to go on her way.
 
I had once more grasped the handle of the tea-pot when I made a rather curious discovery. At the bottom of the tea-cup lay a single lump of sugar. To the majority of persons it would have meant nothing. They would have assumed that they had dropped it in and forgotten it and would have proceeded to pour out the tea. But it happened that, at this time, I did not take sugar in my tea; whence it followed that the lump had not been put in by me. Assuming, therefore, that it had been carelessly dropped in by the waitress, I turned it out on the table, filled the cup, added the milk, and took a tentative draught to test the temperature.
 
The cup was yet at my lips when I chanced to look into the mirror that faced my table. Of course it reflected the part of the shop that was behind me, including the cashier's desk; at which the owner of the basket now stood paying for her refreshment. Between her and me was a gas chandelier which cast its light on my back but full on her face; and her veil notwithstanding, I could see that she was looking at me steadily; was, in fact, watching me intently and with a very curious expression—an expression of expectancy mingled with alarm. But this was not all. As I returned her intent look—which I could do unobserved, since my face, reflected in the mirror, was in deep shadow—I suddenly perceived that that steady gaze engaged her right eye only; the other eye was looking sharply towards her left shoulder. In short, she had a divergent squint of the left eye.
 
I put down my cup with a thrill of amazement and a sudden surging up of suspicion and alarm. An instant's reflection reminded me that when she had spoken to me a few moments before, both her eyes had looked into mine without the slightest trace of a squint. My thoughts flew back to the lump of sugar, to the unguarded milk-jug and the draught of tea that I had already swallowed; and, hardly knowing what I intended, I started to my feet and turned to confront her. But as I rose, she snatched up her change and darted from the shop. Through the glass door, I saw her spring on to the foot-board of a passing hansom and give the driver some direction. I saw the man whip up his horse, and, by the time I reached the door, the cab was moving off swiftly towards Sloane Street.
 
I stood irresolute. I had not paid and could not run out of the shop without making a fuss, and my hat and stick were still on the rail opposite my seat. The woman ought to be followed, but I had no fancy for the task. If the tea that I had swallowed was innocuous, no harm was done and I was rid of my pursuer. So far as I was concerned, the incident was closed. I went back to my seat, and picking up the lump of sugar which still lay on the table where I had dropped it, put it carefully in my pocket. But my appetite for tea was satisfied for the present. Moreover it was hardly advisable to stay in the shop lest some fresh spy should come to see how I fared. Accordingly I obtained my check, handed it in at the cashier's desk and took my departure.
 
All this time, it will be observed, I had been taking it for granted that the lady in black had followed me from Kensington to this shop; that, in fact, she was none other than Mrs. Schallibaum. And, indeed, the circumstances had rendered the conclusion inevitable. In the very instant when I had perceived the displacement of the left eye, complete recognition had come upon me. When I had stood facing the woman, the brief glance at her face had conveyed to me something dimly reminiscent of which I had been but half conscious and had instantly forgotten. But the sight of that characteristic squint had at once revived and explained it. That the woman was Mrs. Schallibaum I now felt no doubt whatever.
 
Nevertheless, the whole affair was profoundly mysterious. As to the change in the woman's appearance, there was little in that. The coarse, black hair might be her own, dyed, or it might be a wig. The eyebrows were made-up; it was a simple enough proceeding and made still more simple by the beaded veil. But how did she come to be there at all? How did she happen to be made-up in this fashion at this particular time? And, above all, how came she to be provided with a lump of what I had little doubt was poisoned sugar?
 
I turned over the events of the day, and the more I considered them the less comprehensible they appeared. No one had followed the omnibus either on foot or in a vehicle, as far as I could see; and I had kept a careful look-out, not only at starting but for some considerable time after. Yet, all the time, Mrs. Schallibaum must have been following. But how? If she had known that I was intending to travel by the omnibus she might have gone to meet it and entered before I did. But she could not have known: and moreover she did not meet the omnibus, for we watched its approach from some considerable distance. I considered whether she might not have been concealed in the house and overheard me mention my destination to Thorndyke. But this failed to explain the mystery, since I had mentioned no address beyond "Kensington." I had, indeed, mentioned the name of Mrs. Hornby, but the supposition that my friends might be known by name to Mrs. Schallibaum, or even that she might have looked the name up in the directory, presented a probability too remote to be worth entertaining.
 
But, if I reached no satisfactory conclusion, my cogitations had one useful effect; they occupied my mind to the exclusion of that unfortunate draught of tea. Not that I had been seriously uneasy after the first shock. The quantity that I had swallowed was not large—the tea being hotter than I cared for—and I remembered that, when I had thrown out the lump of sugar, I had turned the cup upside down on the table; so there could have been nothing solid left in it. And the lump of sugar was in itself reassuring, for it certainly would not have been used in conjunction with any less conspicuous but more incriminating form of poison. That lump of sugar was now in my pocket, reserved for careful examination at my leisure; and I reflected with a faint grin that it would be a little disconcerting if it should turn out to contain nothing but sugar after all.
 
On leaving the tea-shop, I walked up Sloane Street with the intention of doing what I ought to have done earlier in the day. I was going to make perfectly sure that no spy was dogging my footsteps. But for my ridiculous confidence I could have done so quite easily before going to Endsley Gardens; and now, made wiser by a startling experience, I proceeded with systematic care. It was still broad daylight—for the lamps in the tea-shop had been rendered necessary only by the faulty construction of the premises and the dullness of the afternoon—and in an open space I could see far enough for complete safety. Arriving at the top of Sloane Street, I crossed Knightsbridge, and, entering Hyde Park, struck out towards the Serpentine. Passing along the eastern shore, I entered one of the long paths that lead towards the Marble Arch and strode along it at such a pace as would make it necessary for any pursuer to hurry in order to keep me in sight. Half-way across the great stretch of turf, I halted for a few moments and noted the few people who were coming in my direction. Then I turned sharply to the left and headed straight for the Victoria Gate, but again, half-way, I turned off among a clump of trees, and, standing behind the trunk of one of them, took a fresh survey of the people who were moving along the paths. All were at a considerable distance and none appeared to be coming my way.
 
I now moved cautiously fro............