The black eyes of Hassan glared insanely into mine.

“You will have placed them in your pocketcase,” he said.  “Take it out; hand it to me!”

I obeyed, for what else could I do?  Taking the case from my pocket,
I placed it in his lean brown hand.

An expression of wild exultation crossed his features; the eagle eyes seemed to be burning into my brain.  A puff of hot vapour struck me in the face—­something which was expelled from the mysterious black tube.  And with memories crowding to my mind of similar experiences at the hands of the Hashishin, I fell back, clutching at my throat, fighting for my life against the deadly, vaporous thing that like a palpable cloud surrounded me.  I tried to cry out, but the words died upon my tongue.  Hassan of Aleppo seemed to grow huge before my eyes like some ginn of Eastern lore.  Then a curtain of darkness descended.  I experienced a violent blow upon the forehead (I suppose I had pitched forward), and for the time resigned my part in the drama of the sacred slipper.

CHAPTER XXV

THE WATCHER IN BANK CHAMBERS

At about five o’clock that afternoon Inspector Bristol, who had spent several hours in Soho upon the scene of the murder of the Greek, was walking along Fleet Street, bound for the offices of the Report.  As he passed the court, on the corner of which stands a branch of the London County and Provincial Bank, his eye was attracted by a curious phenomenon.

There are reflectors above the bank windows which face the court, and it appeared to Bristol that there was a hole in one of these, the furthermost from the corner.  A tiny beam of light shone from the bank window on to the reflector, or from the reflector on to the window, which circumstance in itself was not curious.  But above the reflector, at an acute angle, this mysterious beam was seemingly projected upward.  Walking a little way up the court he saw that it shone through, and cast a disc of light upon the ceiling of an office on the first floor of Bank Chambers above.

It is every detective’s business to be observant, and although many thousands of passersby must have cast their eyes in the same direction that day, there is small matter for wonder in the fact that Bristol alone took the trouble to inquire into the mystery —­for his trained eye told him that there was a mystery here.

Possibly he was in that passive frame of mind when the brain is particularly receptive of trivial impressions; for after a futile search of the Soho cigar store for anything resembling a clue, he was quite resigned to the idea of failure in the case of Hassan and Company.  He walked down the court and into the entrance of Bank Chambers.  An Inspection of the board upon the wall showed him that the first floor apparently was occupied by three firms, two of them legal, for this is the neighbourhood of the law courts, and the third a press agency.  He stepped up to the first floor.  Past the doors bearing the names of the solicitors and past that belonging to the press agent he proceeded to a fourth suite of offices.  Here, pinned upon the door frame, appeared a card which bore the legend—­