Stuart personally admitted Dunbar, and once more the Inspector found himself in the armchair in the study. The fire was almost out and the room seemed to be chilly. Stuart was labouring under the influence of suppressed excitement and was pacing restlessly up and down the floor.  
"Inspector," he began, "I find it difficult to tell you the facts which have recently come to my knowledge bearing upon this most mysterious 'Scorpion' case. I clearly perceive, now, that without being aware of the fact I have nevertheless been concerned in the case for at least a week."
 
Dunbar stared surprisedly, but offered no comment.
 
"A fortnight ago," Stuart continued, "I found myself in the neighbourhood of the West India Docks. I had been spending the evening with a very old friend, chief officer of a liner in dock. I had intended to leave the ship at about ten o'clock and to walk to the railway station, but, as it fell out, the party did not break up until after midnight. Declining the offer of a berth on board, I came ashore determined to make my way home by tram and afoot. I should probably have done so and have been spared—much; but rain began to fall suddenly and I found myself, foolishly unprovided with a top-coat, in those grey East End streets without hope of getting a lift.
 
"It was just as I was crossing Limehouse Causeway that I observed, to my astonishment, the head-lamps of a cab or car shining out from a dark and forbidding thoroughfare which led down to the river. The sight was so utterly unexpected that I paused, looking through the rainy mist in the direction of the stationary vehicle. I was still unable to make out if it were a cab or a car, and accordingly I walked along to where it stood and found that it was a taxicab and apparently for hire.
 
"'Are you disengaged?' I said to the man. "'Well, sir, I suppose I am,' was his curious reply. 'Where do you want to go?'
 
"I gave him this address and he drove me home. On arriving, so grateful did I feel that I took pity upon the man, for it had settled down into a brute of a night, and asked him to come in and take a glass of grog. He was only too glad to do so. He turned out to be quite an intelligent sort of fellow, and we chatted together for ten minutes or so.
 
"I had forgotten all about him when, I believe on the following night, he reappeared in the character of a patient. He had a badly damaged skull, and I gathered that he had had an accident with his cab and had been pitched out into the road.
 
"When I had fixed him up, he asked me to do him a small favour. From inside his tunic he pulled out a long stiff envelope, bearing no address but the number 30 in big red letters. It was secured at both ends with black wax bearing the imprint of a curious and complicated seal.
 
"'A gentleman left this behind in the cab today, sir,' said the man—'perhaps the one who was with me when I had the spill, and I've got no means of tracing him; but he may be able to trace me if he happened to notice my number, or he may advertise. It evidently contains something valuable.'
 
"'Then why not take it to Scotland Yard?' I asked. 'Isn't that the proper course?'
 
"'It is,' he admitted; 'but here's the point: if the owner reclaims it from Scotland Yard he's less likely to dub up handsome than if he gets it direct from me!'
 
"I laughed at that, for the soundness of the argument was beyond dispute. 'But what on earth do you want to leave it with me for?' I asked."
 
"'Self-protection,' was the reply. 'They can't say I meant to pinch it! Whereas, directly there's any inquiry I can come and collect it and get the reward; and your word will back me up if any questions are asked; that's if you don't mind, sir.'
 
"I told him I didn't mind in the least, and accordingly I sealed the envelope in a yet larger one which I addressed to the Lost Property Office and put into a private drawer of my bureau. 'You will have no objection,' I said, 'to this being posted if it isn't reclaimed within a reasonable time?'
 
"He said that would be all right and departed—since which moment I have not set eyes upon him. I now come to the sequel, or what I have just recognized to be the sequel."
 
Stuart's agitation grew more marked and it was only by dint of a palpable effort that he forced himself to resume.
 
"On the evening of the following day a lady called professionally. She was young, pretty, and dressed with extraordinary elegance. My housekeeper admitted her, as I was out at the time but momentarily expected. She awaited my return here, in this room. She came again two days later. The name she gave was an odd one: Mademoiselle Dorian. There is her card,"—Stuart opened a drawer and laid a visiting-card before Dunbar—"no initials and no address. She travelled in a large and handsome car. That is to say, according to my housekeeper's account it is a large and handsome car. I personally, have had but an imperfect glimpse of it. It does not await her in front of the house, for some reason, but just around the corner in the side turning. Beyond wondering why Mademoiselle Dorian had selected me as her medical advisor I had detected nothing suspicious in her behaviour up to the time of which I am about to speak.
 
"Last night there was a singular development, and to-night matters came to a head."
 
Thereupon Stuart related as briefly as possible the mysterious episode of the cowled man, and finally gave an account of the last visit of Mlle. Dorian. Inspector Dunbar did not interrupt him, but listened attentively to the singular story.
 
"And there," concluded Stuart, "on the blotting-pad, lies the sealed envelope!"
 
Dunbar took it up eagerly. A small hole had been burned in one end of the envelope and much of the surrounding paper was charred. The wax with which Stuart had sealed it had lain uppermost, and although it had been partly melted, the mark of his signet-ring was still discernible upon it. Dunbar stood staring at it.
 
"In the circumstances, Inspector, I think you would be justified in opening both envelopes," said Stuart.
 
"I am inclined to agree. But let me just be clear on one or two points." He took out the bulging note-book and also a fountain-pen with which he prepared to make entries. "About this cabman, now. You didn't by any chance note the number of his cab?"
 
"I did not."
 
"What build of man was he?"
 
"Over medium height and muscular. Somewhat inclined to flesh and past his youth, but active all the same."
 
"Dark or fair?"
 
"Dark and streaked with grey. I noted this particularly in dressing his skull. He wore his hair cropped close to the scalp. He had a short beard and moustache and heavily marked eyebrows. He seemed to be very short-sighted and kept his eyes so screwed up that it was impossible to detect their colour, by night at any rate."
 
"What sort of wound had he on his skull?"
 
"A short ugly gash. He had caught his head on the footboard in falling. I may add that on the occasion of his professional visit his breath smelled strongly of spirits, and I rather suspected that his accident might have been traceable to his condition."
 
"But he wasn't actually drunk?"
 
"By no means. He was perfectly sober, but he had recently been drinking—possibly because his fall had shaken him, of course."
 
"His hands?"
 
"Small and very muscular. Quite steady. Also very dirty."
 
"What part of the country should you say he hailed from?"
 
"London. He had a marked cockney accent."
 
"What make of cab was it?"
 
"I couldn't say."
 
"An old cab?"
 
"Yes. The fittings were dilapidated, I remember, and the cab had a very musty smell."
 
"Ah," said Dunbar, making several notes. "And now—the lady: about what would be her age?"
 
"Difficult to say, Inspector. She had Eastern blood and may have been much younger than she appeared to be. Judged from a European standpoint and from her appearance and manner of dress, she might be about twenty-three or twenty-four."
 
"Complexion?"
 
"Wonderful. Fresh as a flower."
 
"Eyes?"
 
"Dark. They looked black at night."
 
"Hair?"
 
"Brown and 'fuzzy' with copper tints."
 
"Tall?"
 
"No; slight but beautifully shaped."
 
"Now—from her accent what should you judge her nationality to be?"
 
Stuart paced up and down the room, his head lowered in reflection, then:
 
"She pronounced both English and French words with an intonation which suggested familiarity with Arabic."
 
"Arabic? That still leaves a fairly wide field."
 
"It does, Inspector, but I had no means of learning more. She had certainly lived for a long time somewhere in the Near East."
 
"Her jewellery?"
 
"Some of it was European and some of it Oriental, but not characteristic of any particular country of the Orient."
 
"Did she use perfume?"
 
"Yes, but it was scarcely discernible. Jasmine—probably the Eastern preparation."
 
"Her ailment was imaginary?"
 
"I fear so."
 
"H'm—and now you say that Mrs. M'Gregor saw the car?"
 
"Yes, but she has retired."
 
"Her evidence will do to-morrow. We come to the man in the hood. Can you give me any kind of a description of him?"
 
"He appeared to be tall, but a shadow is deceptive, and his extraordinary costume would produce that effect, too. I can tell you absolutely nothing further about him. Remember, I thought I was dreaming. I could not credit my senses."
 
Inspector Dunbar glanced over the notes which he had made, then returning the note-book and pen to his pocket, he took up the long smoke-discoloured envelope and with a paper-knife which lay upon the table slit one end open. Inserting two fingers, he drew out the second envelope which the first enclosed. It was an ordinary commercial envelope only notable by reason of the number, 30, appearing in large red figures upon it and because it was sealed with black wax bearing a weird-looking device:
 
Stuart bent over him intently as he slit this envelope in turn. Again, he inserted two fingers—and brought forth the sole contents… a plain piece of cardboard, roughly rectangular and obviously cut in haste from the lid of a common cardboard box!