During the next day or two my mind constantly reverted to the incidents of the voyage home. I was perfectly convinced that the curtain had been partially raised upon some fantasy in which Professor Deeping figured.
 
But I had seen no more of Deeping nor had I heard from him, when abruptly I found myself plunged again into the very vortex of his troubled affairs. I was half way through a long article, I remember, upon the mystery of the outrage at the docks. The poor steward whose hand had been severed lay in a precarious condition, but the police had utterly failed to trace the culprit.
 
I had laid down my pen to relight my pipe (the hour was about ten at night) when a faint sound from the direction of the outside door attracted my attention. Something had been thrust through the letter-box.
 
"A circular," I thought, when the bell rang loudly, imperatively.
 
I went to the door. A square envelope lay upon the mat—a curious envelope, pale amethyst in colour. Picking it up, I found it to bear my name—written simply—
 
"Mr. Cavanagh."
 
Tearing it open I glanced at the contents. I threw open the door. No one was visible upon the landing, but when I leaned over the banister a white-clad figure was crossing the hall, below.
 
Without hesitation, hatless, I raced down the stairs. As I crossed the dimly lighted hall and came out into the peaceful twilight of the court, my elusive visitor glided under the archway opposite.
 
Just where the dark and narrow passage opened on to Fleet Street I overtook her—a girl closely veiled and wrapped in a long coat of white ermine.
 
"Madam," I said.
 
She turned affrightedly.
 
"Please do not detain me!" Her accent was puzzling, but pleasing. She glanced apprehensively about her.
 
You have seen the moon through a mist?—and known it for what it was in spite of its veiling? So, now, through the cloudy folds of the veil, I saw the stranger's eyes, and knew them for the most beautiful eyes I had ever seen, had ever dreamt of.
 
"But you must explain the meaning of your note!"
 
"I cannot! I cannot! Please do not ask me!"
 
She was breathless from her flight and seemed to be trembling. From behind the cloud her eyes shone brilliantly, mysteriously.
 
I was sorely puzzled. The whole incident was bizarre—indeed, it had in it something of the uncanny. Yet I could not detain the girl against her will. That she went in apprehension of something, of someone, was evident.
 
Past the head of the passage surged the noisy realities of Fleet Street. There were men there in quest of news; men who would have given much for such a story as this in which I was becoming entangled. Yet a story more tantalizingly incomplete could not well be imagined.
 
I knew that I stood upon the margin of an arena wherein strange adversaries warred to a strange end. But a mist was over all. Here, beside me, was one who could disperse the mist—and would not. Her one anxiety seemed to be to escape.
 
Suddenly she raised her veil; and I looked fully into the only really violet eyes I had ever beheld. Mentally, I started. For the face framed in the snowy fur was the most bewitchingly lovely imaginable. One rebellious lock of wonderful hair swept across the white brow. It was brown hair, with an incomprehensible sheen in the high lights that suggested the heart of a blood-red rose.
 
"Oh," she cried, "promise me that you will never breathe a word to any one about my visit!"
 
"I promise willingly," I said; "but can you give me no hint?"
 
"Honestly, truly, I cannot, dare not, say more! Only promise that you will do as I ask!"
 
Since I could perceive no alternative—
 
"I will do so," I replied.
 
"Thank you—oh, thank you!" she said; and dropping her veil again she walked rapidly away from me, whispering, "I rely upon you. Do not fail me. Good-bye!"
 
Her conspicuous white figure joined the hurrying throngs upon the pavement beyond. My curiosity brooked no restraint. I hurried to the end of the courtway. She was crossing the road. From the shadows where he had lurked, a man came forward to meet her. A vehicle obstructed the view ere I could confirm my impression; and when it had passed, neither my lovely visitor nor her companion were anywhere in sight.
 
But, unless some accident of light and shade had deceived me, the man who had waited was Ahmad Ahmadeen!
 
It seemed that some astral sluice-gate was raised; a dreadful sense of foreboding for the first time flooded my mind. Whilst the girl had stood before me it had been different—the mysterious charm of her personality had swamped all else. But now, the messenger gone, it was the purport of her message which assumed supreme significance.
 
Written in odd, square handwriting upon the pale amethyst paper, this was the message—
 
Prevail upon Professor Deeping to place what he has in the brown case in the porch of his house to-night. If he fails to do so, no power on earth can save him from the Scimitar of Hassan.
 
A FRIEND.