By what means were Marden and West struck down?  In thus exposing ourselves, in order that we might trap the author or authors of the outrage, did we act wisely?

“Bristol,” I said suddenly, “it was someone who came through the open window.”

“No one,” he replied, “came through the windows.  West saw absolutely nothing.  But if any one comes that way to-night, we have him!”

“West may have seen nothing; but how else could any one enter?”

Bristol offered no reply; and I plunged again into a maze of speculation.

Powerful mantraps were set in such a way that any one or anything, ignorant of their positions, coming up to the windows must unavoidably be snared.  These had been placed in position with much secrecy after dusk, and the man on duty at the gate stood with his back to the wall.  No one could approach him except from the front.  My thoughts took a new turn.

Was the girl with the violet eyes an ally of the Hashishin?  Thus far, although she so palpably had tricked me, I had found myself unable to speak of her to Bristol; for the idea had entered my mind that she might have learned of the plan to murder Deeping without directly being implicated.  Now came yet another explanation.  The publicity given to that sensational case might have interested some third party in the fate of the stolen slipper!  Could it be that others, in no way connected with the dreadful Hassan of Aleppo, were in quest of the slipper?

Scotland Yard had taken care to ensure that the general public be kept in ignorance of the existence of such an organization as the Hashishin, but I must assume that this hypothetical third party were well aware that they had Hassan, as well as the authorities, to count with.  Granting the existence of such a party, my beautiful acquaintance might be classified as one of its members.  I spoke again.

“Bristol,” I said, “has it occurred to you that there may be others, as well as Hassan of Aleppo, seeking to gain possession of the sacred slipper?”

“It has not,” he replied.  “In the strictest sense of the expression, they would be out for trouble!  What gave you the idea?”

“I hardly know,” I returned evasively, for even now I was loath to betray the mysterious girl with the wonderful eyes.

The chapel bell sounding the half-hour, Bristol rose with a sigh that might have been one of relief, and went out to take the report of the man on duty at the gate.  As his footsteps died away along the elm avenue, it came to me how, in the darkness about, menace lurked; and I felt myself succumbing to the greatest dread experienced by man—­the dread of the unknown.

All that I knew of the weird group of fanatics—­survivals of a dim and evil past—­who must now be watching this cottage as bloodlustful devotees watch a shrine violated, burst upon my mind.  I peopled the still blackness with lurking assassins, armed with the murderous knowledge of by-gone centuries, armed with invisible weapons which struck down from afar, supernaturally.