“How deeply gratified and flattered those great personages would have felt,” I remarked, “if they had known how much attention they were receiving.”

“Yes; I suppose it would have been somewhat startling, to the Prime Minister, for instance, to have learned that he was being watched and studied by an attentive observer and that the arrangements for his decease had been completed down to the minutest detail.  But, of course, the application of the method to a particular case was the essential thing, for it brought into view all the incidental difficulties, in meeting which all the really interesting and instructive details were involved.  Well, the particulars of these crimes I wrote out at length, in my private shorthand, in a journal which I kept for the purpose—­and which, I need not say, I locked up securely in my safe when I was not using it.  After completing each case, it was my custom to change sides and play the game over again from the opposite side of the board; that is to say, I added, as an appendix to each case, an analysis with a complete scheme for the detection of the crime.  I have in my safe at the present moment six volumes of cases, fully indexed; and I can assure you that they are not only highly instructive reading, but are really valuable as works of reference.”

“That I can readily believe,” I replied, laughing heartily, nevertheless, at the grotesqueness of the whole proceeding, “though they might have proved rather incriminating documents if they had passed out of your possession.”

“They would never have been read,” rejoined Thorndyke.  “My shorthand is, I think, quite undecipherable; it has been so made intentionally with a view to secrecy.”

“And have any of your theoretical cases ever turned up in real life?”

“Several of them have, though very imperfectly planned and carried out as a rule.  The poisoned cigar is one of them, though, of course I should never have adopted such a conspicuous device for presenting it; and the incident of the other night is a modification—­for the worse—­of another.  In fact, most of the intricate and artistic crimes with which I have had to deal professionally have had their more complete and elaborate prototypes in my journals.”

I was silent for some time, reflecting on the strange personality of my gifted friend and the singular fitness that he presented for the part he had chosen to play in the drama of social life; but presently my thoughts returned to the peril that overshadowed him, and I came back, once more, to my original question.

“And now, Thorndyke,” I said, “that you have penetrated both the motives and the disguise of this villain, what are you going to do?  Is he to be put safely under lock and key, or is he to be left in peace and security to plan some other, and perhaps more successful, scheme for your destruction?”

“For the present,” replied Thorndyke, “I am going to put these things in a place of safety.  To-morrow you shall come with me to the hospital and see me place the ends of the cigar in the custody of Dr. Chandler, who will make an analysis and report on the nature of the poison.  After that we shall act in whatever way seems best.”