"There's no doubt in my mind," said Inspector Bristol, "that your experience was real enough."  
The sun was shining into my room now, but could not wholly disperse the cloud of horror which lay upon it. That I had been drugged was sufficiently evident from my present condition, and that I had been taken away from my chambers Inspector Bristol had satisfactorily proved by an examination of the soles of my slippers.
 
"It was a clever trick," he said. "God knows what it was they puffed into your face through the letter box, but the devilish arts of ten centuries, we must remember, are at the command of Hassan of Aleppo! The repetition of the trick at the mysterious place you were taken to is particularly interesting. I should say you won't be in a hurry to peer through letter boxes and so forth in the future?"
 
I shook my aching head.
 
"That accursed yellow room," I replied, "stank with the fumes of hashish. It may have been some preparation of hashish that was used to drug me."
 
Bristol stood looking thoughtfully from the window.
 
"It was a nightmare business, Mr. Cavanagh," he said; "but it doesn't advance our inquiry a little bit. The prophecy of the old man with the white beard—whom you assure me to be none other than Hassan of Aleppo—is something we cannot very well act upon. He clearly believes it himself; for he has released you after having captured you, evidently in order that you may be at liberty to take up your duty as trustee of the slipper again. If the slipper really comes back to the Museum the fact will show Hassan to be something little short of a magician. I shan't envy you then, Mr. Cavanagh, considering that you hold the keys of the case!"
 
"No," I replied wearily. "Poor Professor Deeping thought that he acted in my interests and that my possession of the keys would constitute a safeguard. He was wrong. It has plunged me into the very vortex of this ghastly affair."
 
"It is maddening," said Bristol, "to know that Hassan and Company are snugly located somewhere under our very noses, and that all Scotland Yard can find no trace of them. Then to think that Hassan of Aleppo, apparently by means of some mystical light, has knowledge of the whereabouts of the slipper and consequently of the whereabouts of Earl Dexter (another badly wanted man) is extremely discouraging! I feel like an amateur; I'm ashamed of myself!"
 
Bristol departed in a condition of irritable uncertainty.
 
My head in my hands, I sat for long after his departure, with the phantom characters of the ghoulish drama dancing through my brain. The distorted yellow dwarfs seemed to gibe apish before me. Severed hands clenched and unclenched themselves in my face, and gleaming knives flashed across the mental picture. Predominant over all was the stately figure of Hassan of Aleppo, that benignant, remorseless being, that terrible guardian of the holy relic who directed the murderous operations. Earl Dexter, The Stetson Man, with his tightly bandaged arm, his gaunt, clean-shaven face and daredevil smile, figured, too, in my feverish daydream; nor was that other character missing, the girl with the violet eyes whose beautiful presence I had come to dread; for like a sybil announcing destruction her appearances in the drama had almost invariably presaged fresh tragedies. I recalled my previous meetings with this woman of mystery. I recalled my many surmises regarding her real identity and association with the case. I wondered why in the not very distant past I had promised to keep silent respecting her; I wondered why up to that present moment, knowing beyond doubt that her activities were inimical to my interests, were criminal, I had observed that foolish pledge.
 
And now my door-bell was ringing—as intuitively I had anticipated. So certain was I of the identity of my visitor that as I walked along the passage I was endeavouring to make up my mind how I should act, how I should receive her.
 
I opened the door; and there, wearing European garments but a green turban ... stood Hassan of Aleppo!
 
When I say that amazement robbed me of the power to speak, to move, almost to think, I doubt not you will credit me. Indeed, I felt that modern London was crumbling about me and that I was become involved in the fantastic mazes of one of those Oriental intrigues such as figure in the Romance of Abu Zeyd, or with which most European readers have been rendered familiar by the glowing pages of "The Thousand and One Nights."
 
"Effendim," said my visitor, "do not hesitate to act as I direct!"
 
In his gloved hand he carried what appeared to be an ebony cane. He raised and pointed it directly at me. I perceived that it was, in fact, a hollow tube.
 
"Death is in my hand," he continued; "enter slowly and I will follow you."
 
Still the sense of unreality held me thralled and my brain refused me service. Like an hypnotic subject I walked back to my study, followed by my terrible visitor, who reclosed the door behind him.
 
He sat facing me across my littered table with the mysterious tube held loosely in his grasp.
 
How infinitely more terrifying are perils unknown than those known and appreciated! Had a European armed with a pistol attempted a similar act of coercion, I cannot doubt that I should have put up some sort of fight; had he sat before me now as Hassan of Aleppo sat, with a comprehensible weapon thus laid upon his knees, I should have taken my chance, should have attacked him with the lamp, with a chair, with anything that came to my hand.
 
But before this awful, mysterious being who was turning my life into channels unsuspected, before that black tube with its unknown potentialities, I sat in a kind of passive panic which I cannot attempt to describe, which I had never experienced before and have never known since.
 
"There is one about to visit you," he said, "whom you know, whom I think you expect. For it is written that she shall come and such events cast a shadow before them. I, too, shall be present at your meeting!"
 
His eagle eyes opened widely; they burned with fanaticism.
 
"Already she is here!" he resumed suddenly, and bent as one listening. "She comes under the archway; she crossed the courtyard—and is upon the stair! Admit her, effendim; I shall be close behind you!"
 
The door-bell rang.
 
With the consciousness that the black tube was directed toward the back of my head, I went and opened the door. My mind was at work again, and busy with plans to terminate this impossible situation.
 
On the la............