"In this way, and as a negative test. The alibi is a commonplace of the criminal courts. Every person on whom clues might ultimately rest would be eliminated from the investigation if it could be proved beyond doubt that they were elsewhere at the time. You must remember, that we had not only to find the murderer, but to produce evidence that would satisfy a jury that we were right. But we worked, first of all, from such main facts as we had. You were missing. Ivan was missing. A mysterious veiled woman was missing. There was the pearl necklace that you had bought as a wedding present for Lady Eileen. There was the strange dagger used in the murder. There was the miniature of Lola on the dead man. These were the chief heads. There were scores of minor things to be dealt with. "The matter was complicated, too, by the dead man's clothes. In the pockets, there were your personal belongings. A natural, but erroneous assumption was that they were your clothes. There is not much scope for individuality in evening dress. I confess I was misled and puzzled at first, but a little thought afforded the explanation, and, in fact, it would have been cleared up automatically in any event by the examination of the garments. "Now, subtlety may be an admirable thing, but it can be overdone. I have never believed that, because a certain thing seems obvious, it is necessarily wrong. It was reasonably certain that one, or all of the missing persons, had knowledge of what had happened. It was extremely probable that one of them was guilty. Our starting-point was to find them. That was where organisation came in. The miniature helped me to bluff Sir Ralph Fairfield into an admission that it was the portrait of Lola of Vienna, and I purposely showed it to some newspaper men on a pretext. One of them commented on the likeness to the Princess Petrovska, who was staying at the Hotel Palatial, and I at once telephoned to the hotel, and discovered that she was supposed to have left at ten on the evening of the murder. A reference to the St. Petersburg police gave us a few more facts about her. She became a possibility as the veiled visitor. "The finger-prints on the dagger, although we should have adopted a different method had we known what we know now, helped us to narrow the investigation, for they apparently--and actually by luck--settled the innocence of several people who might have been suspected. "Lady Eileen Meredith came to me with a story that seemed to implicate Sir Ralph Fairfield. There seemed just a possibility that she was right, for I could conceive jealousy might be a motive--though, of course, there was so far nothing to explain why the master of the house and his valet should take to flight. I took Sir Ralph's finger-prints by a ruse, and to me that seemed fairly satisfactory proof that he was not the man. Of course, I was then presuming that the finger-prints were those of the murderer.