"It is in the hope that no payment may ever be demanded of you," he rejoined, "that I am busying myself in your affairs." The colour sprang to Gwen's cheeks, but she only replied by a grateful glance. I knew what was passing through her mind. She was thinking of her promise--of her father's last words, and of the terrible possibilities thereof from which Maitland was seeking to rescue her. She felt that she could safely owe him any debt of gratitude, however great, while he, on his part, took what I fancied, both then and afterward, were unnecessary pains to assure her that, in the event of his finding the assassin, she need have no fear of his making any claim whatsoever upon her. And so the whole affair was dropped for the time being and the rest of the evening devoted to listening to Maitland's account of his experiences while abroad.
The next morning I called upon our detective at his laboratory and asked him what he intended to do next. He replied that he had no plans as yet, but that he wished to review with me all the evidence at hand.
"You see," he said, "the thing that renders the solution of this mystery so difficult is the fact that all our clues, while they would be of the utmost service in the conviction of the assassin had we found him, are almost destitute of any value until he has been located. Add to this that we are now unable to find any motive for the crime and you can see how slight are our hopes of success. If ever we chance to find the man,--for I feel that such a consummation would result more from chance than from anything else,--I think we can convict him.
"Here, for example," he said, taking up a small slip of glass which he had cut from the eastern parlour window of the Darrow house, "is something I have never shown either you or Miss Darrow. It is utterly worthless, so far as assisting us to track the assassin is concerned, but, if ever we suspect the right man, the evidence on that glass would probably convict him, though there were ten thousand other suspects."
I took the glass from him and, examining it with the utmost care, I detected a smutch of yellowish paint upon it, nothing more. "For Heaven's sake, Maitland!" I said in astonishment, "of what possible use can that formless daub of paint be, or is there something else on the glass that has escaped me?" He laughed at my excitement as he replied: "There is nothing there but the paint spot. Regarding that, however, you have come to a very natural though erroneous conclusion. It is not formless"; and he passed me a jeweller's eye-glass to assist me in a closer examination. He was right. The paint lay upon the glass in little irregular furrows which arranged themselves concentrically about a central oval groove somewhat imperfect in shape. "Well," continued. Maitland, as I returned him the magnifying glass, "what do you make of it?" "If you hadn't already attached so much importance to the thing," I said, "I should pronounce it a daub of paint transferred to the glass by somebody's thumb, but, as such a thing would be clearly useless, I am at a loss to know what it is."