“And very justifiably.  You see now how completely you were in the right when you allowed yourself to entertain this theory of the crime in spite of its apparent improbability.  By the light of these new facts it has become quite a probable explanation of the whole affair, and if it could only be shown that Mr. Hornby’s memorandum block was among the papers on the table, it would rise to a high degree of probability.  The obvious moral is, never disregard the improbable.  By the way, it is odd that Reuben failed to recall this occurrence when I questioned him.  Of course, the bloody finger-marks were not discovered until he had gone, but one would have expected him to recall the circumstance when I asked him, pointedly, if he had never left bloody finger-prints on any papers.”

“I must try to find out if Mr. Hornby’s memorandum block was on the table and among the marked papers,” I said.

“Yes, that would be wise,” he answered, “though I don’t suppose the information will be forthcoming.”

My colleague’s manner rather disappointed me.  He had heard my report with the greatest attention, he had discussed it with animation, but yet he seemed to attach to the new and—­as they appeared to me—­highly important facts an interest that was academic rather than practical.  Of course, his calmness might be assumed; but this did not seem likely, for John Thorndyke was far too sincere and dignified a character to cultivate in private life the artifices of the actor.  To strangers, indeed, he presented habitually a calm and impassive exterior; but this was natural to him, and was but the outward sign of his even and judicial habit of mind.

No; there was no doubt that my startling news had left him unmoved, and this must be for one of two reasons:  either he already knew all that I had told him (which was perfectly possible), or he had some other and better means of explaining the crime.  I was turning over these two alternatives, not unobserved by my watchful colleague, when Polton entered the room; a broad grin was on his face, and a drawing-board, that he carried like a tray, bore twenty-four neatly turned boxwood pieces.

Thorndyke at once entered into the unspoken jest that beamed from the countenance of his subordinate.

“Here is Polton with a problem for you, Jervis,” he said.  “He assumes that I have invented a new parlour game, and has been trying to work out the moves.  Have you succeeded yet, Polton?”

“No, sir, I haven’t; but I suspect that one of the players will be a man in a wig and gown.”

“Perhaps you are right,” said Thorndyke; “but that doesn’t take you very far.  Let us hear what Dr. Jervis has to say.”

“I can make nothing of them,” I answered.  “Polton showed me the drawing this morning, and then was terrified lest he had committed a breach of confidence, and I have been trying ever since, without a glimmer of success, to guess what they can be for.”