He plunged off toward the open door, and I heard him racing down the Assyrian Room.

“He had a short rope ladder fixed from the gutter!” he cried back at us.  “Graham!  Graham!” (the constable on duty in the hall)—­ “Get the front door open!  Get . . . " His voice died away as he leapt down the stairs.

From the direction of Orpington Square came a horrid, choking scream.  It rose hideously; it fell, rose again—­and died.

The thief escaped.  We saw the traces upon the ivy where he had hastened down.  Bristol ascended by the same route, and found where the ladder-hooks had twice been attached to the gutterway.  Constable Graham, who was first actually to leave the building, declared that he heard the whirr of a re-started motor lower down Great Orchard Street.

Bristol’s theory, later to be dreadfully substantiated, was that the thief had broken the glass and reached into the case with an arrangement similar to that employed for pruning trees, having a clutch at the end, worked with a cord.

“Hassan has been too clever for us!” said the inspector.  “But—­ what in God’s name did that awful screaming mean?”

I had a theory, but I did not advance it then.

It was not until nearly dawn that my theory, and Bristol’s, regarding the clutch arrangement, both were confirmed.  For close under the railings which abut on Orpington Square, in a pool of blood we found just such an instrument as Bristol had described.

And still clutching it was a pallid and ghastly shrunken hand that had been severed from above the wrist!

“Merciful God!” whispered the inspector—­“look at the opal ring on the finger!  Look at the bandage where he cut himself on the broken window-glass that first night, when Mr. Mostyn disturbed him.  It wasn’t the Hashishin who stole the thing . . . .  It’s Earl Dexter’s hand!”

No one spoke for a moment.  Then—­

“Which of them has—­” began Mostyn huskily.

“The slipper of the Prophet?” interrupted Bristol.  “I wonder if we shall ever know?”

CHAPTER XV

A SHRIVELLED HAND

Around a large square table in a room at New Scotland Yard stood a group of men, all of whom looked more or less continuously at something that lay upon the polished deal.  One of the party, none other than the Commissioner himself, had just finished speaking, and in silence now we stood about the gruesome object which had furnished him with the text of his very terse address.

I knew myself privileged in being admitted to such a conference at the C.I.D. headquarters and owed my admission partly to Inspector Bristol, and partly to the fact that under the will of the late Professor Deeping I was concerned in the uncanny business we were met to discuss.