‘In setting to work to read the riddle, I proceeded on the analytical principle, and searched, to begin with, for the motive. That seemed very apparent. Firstly, it was a secret treaty; secondly, it was framed against Turkey; thirdly, it was conceivable that it was of vital importance to Turkey to know what the treaty was likely to do, what it aimed at; therefore, somebody in the pay of Turkey, or somebody as a speculation, had stolen the document with a view to pecuniary gain.

‘The latter supposition seemed to me hardly tenable—at any rate, not so likely as the idea that Turkey had her spies even in the Russian Foreign Office. I don’t mean to say these spies were Turks themselves. As can be understood, it would have been next to impossible for a Turk to have gained entrance to the Foreign Office; but Turkey, of course, had her emissaries, and Russians were to be found so debased, so dead to all patriotism, so lost to every sense of honour, so mercenary, that they were ready to sell their country for the gain of gold. Of course, black sheep of this kind are numbered in every nation, therefore Russia was no exception.

‘Everything pointed to the thief being a Russian, and, being a Russian, he also had some connection with the Foreign Office, a connection which gave him the right of being under the roof all night.

‘It is necessary to explain that the Foreign Minister in Russia is provided with an official residence in the Foreign Office itself; that is to say, a portion of the actual building is set apart for the accommodation of himself and family and suite. An official of this kind keeps up a great deal more state than an English Minister does, and his suite and servants are generally very numerous.

‘In the Prince’s case, there were fewer people about him than usual, for the reason that he had no family. Nevertheless, I found that, including footmen, pages, and lower servants, there were forty persons in his ménage, and his domestic affairs were attended to and presided over by the lady whom he had addressed as Catarina, and whose ravishing beauty had so struck me. It is not necessary to refer to her by any other name. This lady had two private maids, and she exercised very considerable influence over the Prince’s personal and domestic affairs.

‘At this stage of my theorizing it seemed to me very clear that the miscreant would be found amongst the personnel of the Prince. The consideration of all the facts forced me to this, the most feasible conclusion. But I did not lose sight of the almost absolute certainty of a conspiracy, because it was hardly conceivable that one person, and one person only, would have committed such a daring act of treason; for an act of that kind was very foul treason indeed, and in Russia was punishable with death.

‘Assuming that I was right with regard to my surmises, it would seem that a member of the household had been tampered with; pressure and temptation had been brought to bear upon him from outside. The temptation must have been great; heavy payment would be made; the traitor had been willing to sell his country for blood-money, and I was at pains to try and ascertain if any member of the Prince’s personnel had given indications of being in possession of an unusual amount of money.

‘I have endeavoured so far to make clear to those who may read this narrative the mental process by which I tried to lay hold of a clue. I need scarcely say that at the outset in a case of this kind one gropes in the dark. There is not a ray of light at first to guide him, and he must proceed cautiously and warily lest he go astray, and, while he is straining his eyes in one direction, his quarry is safely flying in another. Seeming impossibilities have to be reconciled with probabilities, and probabilities reduced to certainties. And when a clue, no matter how faint, has once been struck, it must be followed up patiently, intelligibly, and doggedly. There are three golden rules to be strictly observed by him who would succeed in connecting crime with its author. They are patience, silence, watchfulness.

‘Human craft and human cunning are very difficult things to deal with, nor can one deal with them at all unless he is deeply read in human nature. In this instance craft of no ordinary kind had to be encountered. The criminal, to begin with, was not of the ordinary type. It was probable that up to this time he had lived a seeming virtuous life, and knowing how terrible was the penalty attaching to his wrong-doing, he would strain every nerve to prevent suspicion falling upon him. I had necessarily to consider all these little details, for they were essential to success.

‘Although the Prince bore the reputation of being a cool, calculating diplomatist, who had outwitted every other diplomatist in Europe with whom he had had dealings, I found that in this matter of the stolen treaty he somewhat discredited his reputation; for he was by no means cool, and seemed unable to enter into the calculations which were necessary to a clear understanding of the course to be pursued if the mystery was to be unravelled. He had at the outset reminded me that I had the resources of an empire at my command, and he insisted on the telegraph being set instantly to work, and the police throughout the country being placed in possession of the facts. I was opposed to that course myself; I thought it was as likely as not to frustrate our efforts. But, of course, he had his own way, and he soon began to display not only irritation, but decided anger, when he found that I narrowed my search to the Foreign Office, and showed no inclination to go further afield. “It seems to me,” he cried warmly, “that you are simply wasting time, and giving the enemy a chance. While you are hanging about here the traitor is making good his escape. Is it not certain that, whoever it is who stole the document, he is now hurrying to Turkey with it as fast as he can?”