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.