“Thanks,” drawled Dexter, nodding to his companion, who went into the outer office, where she might be heard lowering the windows.  She was gone but a few moments ere she returned again, carrying a length of knotted rope.  Under cover of Dexter’s revolver, Bristol stoically submitted to having his wrists tied behind him.  The end of the line was then thrown through the ventilator above the door which communicated with the outer office and Bristol was triced up in such a way that, his wrists being raised behind him to an uncomfortable degree, he was almost forced to stand upon tiptoe.  The line was then secured.

“Very workmanlike!” commented the victim.  “You’ll find a large handkerchief in my inside breast pocket.  It’s a clean one, and I can recommend it as a gag!”

Very promptly it was employed for the purpose, and Inspector Bristol found himself helpless and constrained in a very painful position.  Dexter laid down his revolver.

“We will now give you a free show, Inspector,” he said, genially, “of our camera obscura!”

He pulled down the blinds, which Bristol noted with interest to be black, but through an opening in one of them a mysterious ray of light—­the same that he had noticed from Fleet Street—­shone upon that point in the ceiling where the arrangement of mirrors was attached.  Dexter made some alteration, apparently in the focus of the lens (for Bristol had divined that in some way a lens had been fixed in the reflector above the bank window below) and the disc of light became concentrated.  The white-covered table was moved slightly, and in the darkness some further manipulation was performed.

“Observe,” came the strident voice—­“we now have upon the screen here a minute moving picture.  This little device, which is not protected in any way, is of my own invention, and proved extremely useful in the Arkwright jewel case, which startled Chicago.  It has proved useful now.  I know almost as much concerning the arrangements below as the manager himself.  In confidence, Inspector, this is my last bid for the slipper!  I have plunged on it.  Madame Sforza, the distinguished Italian lady who recently opened an account below, opened it for 500 pounds cash.  She has drawn a portion, but a balance remains which I am resigned to lose.  Her motor-car (hired), her references (forged), the case of jewels which she deposited this morning (duds!)—­all represent a considerable outlay.  It’s a nerve-racking line of operation, too.  Any hour of the day may bring such a visitor as yourself, for example.  In short, I am at the end of my tether.”

Bristol, ignoring the increasing pain in his arms and wrists, turned his eyes upon the white-covered table and there saw a minute and clear-cut picture, such as one sees in a focussing screen, of the interior of the manager’s office of the London County and Provincial Bank!

CHAPTER XXVI