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.

CHAPTER III

“Hassan of Aleppo”

Professor Deeping’s number was in the telephone directory, therefore, on returning to my room, where there still lingered the faint perfume of my late visitor’s presence, I asked for his number.  He proved to be at home.

“Strange you should ring me up, Cavanagh,” he said; “for I was about to ring you up.”

“First,” I replied, “listen to the contents of an anonymous letter which I have received.”

(I remembered, and only just in time, my promise to the veiled messenger.)

“To me,” I added, having read him the note, “it seems to mean nothing.  I take it that you understand better than I do.”