“If a duplicate key to the safe—­” another voice struck in; I knew it afterward for that of Professor Rhys-Jenkyns.

“Impossible to procure one, Professor,” cried Mostyn, his eyes sparkling with an almost boyish interest.  “Mr. Cavanagh here holds the keys of the case, under the will of the late Professor Deeping.  They are of foreign workmanship and more than a little complicated.”

The eyes of the savants were turned now in my direction.

“I suppose you have them in a place of safety?” said Dr. Nicholson.

“They are at my bankers,” I replied.

“Then I venture to predict,” said the celebrated Orientalist, “that the slipper of the Prophet will rest here undisturbed.”

He linked his arm into that of a brother scholar and the little group straggled away, Mostyn accompanying them to the main entrance.

But I saw Inspector Bristol scratching his chin; he looked very much as if he doubted the accuracy of the doctor’s prediction.  He had already had some experience of the implacable devotion of the Moslem group to this treasure of the Faithful.

“The real danger begins,” I suggested to him, “when the general public is admitted—­after to-day, is it not?”

“Yes.  All to-day’s people are specially invited, or are using special invitation cards,” he replied.  “The people who received them often give their tickets away to those who will be likely really to appreciate the opportunity.”

I looked around for the tall Oriental.  He seemed to have vanished, and for some reason I hesitated to speak of him to Bristol; for my gaze fell upon an excessively thin, keen-faced man whose curiously wide-open eyes met mine smilingly, whose gray suit spoke Stein-Bloch, whose felt was a Boss raw-edge unmistakably of a kind that only Philadelphia can produce.  At the height of the season such visitors are not rare, but this one had an odd personality, and moreover his keen gaze was raking the place from ceiling to floor.

Where had I met him before?  To the best of my recollection I had never set eyes upon the man prior to that moment; and since he was so palpably an American I had no reason for assuming him to be associated with the Hashishin.  But I remembered—­indeed, I could never forget—­how, in the recent past, I had met with an apparent associate of the Moslems as evidently European as this curiously alert visitor was American.  Moreover . . . there was something tauntingly familiar, yet elusive, about that gaunt face.

Was it not upon the eve of the death of Professor Deeping that the girl with the violet eyes had first intruded her fascinating personality into my tangled affairs?  Patently, she had then been seeking the holy slipper, and by craft had endeavoured to bend me to her will.  Then had I not encountered her again, meeting the glance of her unforgettable violet eyes outside a Strand hotel?  The encounter had presaged a further attempt upon the slipper!  Certainly she acted on behalf of someone interested in it; and since neither Bristol nor I could conceive of any one seeking to possess the bloodstained thing except the mysterious leader of the Hashishin—­Hassan of Aleppo—­as a creature of that awful fanatic being I had written her down.