What sort of relations were growing up between Juliet Gibson and me?  And what was my position?  As to hers, it seemed plain enough; she was wrapped up in Reuben Hornby and I was her very good friend because I was his.  But for myself, there was no disguising the fact that I was beginning to take an interest in her that boded ill for my peace of mind.

Never had I met a woman who so entirely realised my conception of what a woman should be, nor one who exercised so great a charm over me.  Her strength and dignity, her softness and dependency, to say nothing of her beauty, fitted her with the necessary weapons for my complete and utter subjugation.  And utterly subjugated I was—­there was no use in denying the fact, even though I realised already that the time would presently come when she would want me no more and there would remain no remedy for me but to go away and try to forget her.

But was I acting as a man of honour?  To this I felt I could fairly answer “yes,” for I was but doing my duty, and could hardly act differently if I wished to.  Besides, I was jeopardising no one’s happiness but my own, and a man may do as he pleases with his own happiness.  No; even Thorndyke could not accuse me of dishonourable conduct.

Presently my thoughts took a fresh turn and I began to reflect upon what I had heard concerning Mr. Hornby.  Here was a startling development, indeed, and I wondered what difference it would make in Thorndyke’s hypothesis of the crime.  What his theory was I had never been able to guess, but as I walked along through the thickening fog I tried to fit this new fact into our collection of data and determine its bearings and significance.

In this, for a time, I failed utterly.  The red thumb-mark filled my field of vision to the exclusion of all else.  To me, as to everyone else but Thorndyke, this fact was final and pointed to a conclusion that was unanswerable.  But as I turned the story of the crime over and over, there came to me presently an idea that set in motion a new and very startling train of thought.

Could Mr. Hornby himself be the thief?  His failure appeared sudden to the outside world, but he must have seen difficulties coming.  There, indeed, was the thumb-mark on the leaf which he had torn from his pocket-block.  Yes! but who had seen him tear it off?  No one.  The fact rested on his bare statement.

But the thumb-mark?  Well, it was possible (though unlikely)—­still possible—­that the mark might have been made accidentally on some previous occasion and forgotten by Reuben, or even unnoticed.  Mr. Hornby had seen the “Thumbograph,” in fact his own mark was in it, and so would have had his attention directed to the importance of finger-prints in identification.  He might have kept the marked paper for future use, and, on the occasion of the robbery, pencilled a dated inscription on it, and slipped it into the safe as a sure means of diverting suspicion.  All this was improbable in the highest degree, but then so was every other explanation of the crime; and as to the unspeakable baseness of the deed, what action is too base for a gambler in difficulties?