Mr. Gryce did not think it worth his while to answer. Perhaps he had not time; for leaving the valet where he was, and Miss Butterworth where she was (only she would not be left, but followed him), he made his way upstairs, and paused at the place she had mentioned, with a curious look at the floor. "You see, it has been much trodden here," she said; at which gentle reminder of her presence he gave a start; possibly he had not heard her behind him, and after sixty years of hard service even a detective may be excused a slight nervousness. "Now, why should it be trodden here? There is no apparent reason why any one should shuffle to and fro in this corner. The stair is wide, especially here, and there is no window----" Mr. Gryce, whose eye had been travelling over the wall, reached over her shoulder to one of the dozen pictures hanging at intervals from the bottom to the top of the staircase, and pulling it away from the wall, on which it hung decidedly askew, revealed a round opening through which poured a ray of blue light which could only proceed from the vault of the adjoining study. "No window," he repeated. "No, but an opening into the study wall which answers the same purpose. Miss Butterworth, your eye is to be trusted every time. I only wonder you did not pull this picture aside yourself." "It was not hanging crooked then. Besides I was in a hurry. I had just come from my encounter with this demented man. I had noticed the marks on the landing, and the worn edges of the carpet, on my way upstairs. I was in no condition to observe them on my way down." "I see." Miss Butterworth ran her foot to and fro over the flooring they were examining. "Bartow was evidently in the habit of coming here constantly," said she, "probably to learn whether his master had need of him. Ingenious in Mr. Adams to contrive signals for communication with this man! He certainly had great use for his deaf-and-dumb servant. So one mystery is solved!" "And if I am not mistaken, we can by a glance through this loophole obtain the answer to another. You are wondering, I believe, how Bartow, if he followed the movements of the assailant from the doorway, came to thrust with his left hand, instead of with his right. Now if he saw the tragedy from this point, he saw it over the assailant's shoulder, instead of face to face. What follows? He would imitate literally the movements of the man he saw, turn in the same direction and strike with the same hand." "Mr. Gryce, we are beginning to untangle the threads that looked so complicated. Ah, what is that? Why, it's that bird! His cage must be very nearly under this hole." "A little to one side, madam, but near enough to give you a start. What was it he cried then?" "Oh, those sympathetic words about Eva! 'Poor Eva!'" "Well, give a glance to Bartow. You can see him very well from here."