“No work at all!” returned the boy indignantly.  “I’m just here for a blessed buffer, that’s what I’m here for, a buffer!”

“What do you mean?”

“I just have to sit here and see that nobody gets into that office.  Lively, ain’t it?  Where’s the prospects?”

Bristol surveyed him thoughtfully.

“Look here, my lad,” he said quietly; “is that door locked?”

“Always,” replied the boy.

“Does Mr. Knowlson come to that shutter when you knock?”

“Yes.”

“Then go and knock!”

The boy obeyed with alacrity.  He rapped loudly on the door, not noticing or not caring that the visitor was standing directly behind him.  The shutter was lowered and a grizzled, bearded face showed for a moment through the opening.

Bristol leant over the boy and pushed a card through into the hand of the man beyond.  On this occasion it did not bear the legend “John Henry Smith,” but the following—­

Chief inspector Bristol
C.I.D. 
New Scotland yard

“Good afternoon, Mr. Knowlson,” said the detective dryly.  “I want to come in!”

There followed a moment of silence, from which Bristol divined that he had blundered upon some mystery, possibly upon a big case; then a key was turned in the lock and the door thrown open.

“Come right in, Inspector,” invited a strident voice.  “Carter, you can go home.”

Bristol entered warily, but not warily enough.  For as the door was banged upon his entrance he faced around only in time to find himself looking down the barrel of a Colt automatic.

With his back to the door which contained the wicket, now reclosed, stood the man with the bearded face.  The revolver was held in his left hand; his right arm terminated in a bandaged stump.  But without that his steel-gray eyes would have betrayed him to the detective.

“Good God!” whispered Bristol.  “It’s Earl Dexter!”

“It is!” replied the cracksman, “and you’ve looked in at a real inconvenient time!  My visitors mostly seem to have that knack.  I’ll have to ask you to stay, Inspector.  Sit down in that chair yonder.”

Bristol knew his man too well to think of opening any argument at that time.  He sat down as directed, and ignoring the revolver which covered him all the time, began coolly to survey the room in which he found himself.  In several respects it was an extraordinary apartment.

The only bright patch in the room was the shining disc upon the ceiling; and the detective noted with interest that this marked the position of an arrangement of mirrors.  A white-covered table, entirely bare, stood upon the floor immediately beneath this mysterious apparatus.  With the exception of one or two ordinary items of furniture and a small hand lathe, the office otherwise was unfurnished.  Bristol turned his eyes again upon the daring man who so audaciously had trapped him—­the man who had stolen the slipper of the Prophet and suffered the loss of his hand by the scimitar of an Hashishin as a result.  When he had least expected to find one, Fate had thrown a clue in Bristol’s way.  He reflected grimly that it was like to prove of little use to him.