"Which one of the men or women known to be in the museum when this arrow was released has enough knowledge of archery to string a bow? A mark can be reached by chance; but only an accustomed hand can string a bow as unyielding as this one. "Who telephoned to Madame Duclos; and of what nature was the message which sent her from the hotel so precipitately that she not only left the most important part of her baggage behind but went away without making adequate provision for the young girl confided to her charge? "Does this mean that she had been made acquainted with the fate of the young girl; and if so, by whom?" "Business enough for us all," was the Inspector's comment as Gryce paused in this enumeration. "As you put it, I am more and more convinced that the key you spoke of a short time ago will be found in this missing woman's tightly shut hand." "Which brings us round full-circle to our first conclusion: that Miss Willetts' death is not only a crime, but a premeditated one." "Carried out, not by the one benefited, but by an agent selected for the purpose." "An agent, moreover, who knew the ways and possibilities of the place." "A logical conclusion; but still too incredible for belief. I find it hard to trust to appearances in this case." "And I also. But as we have both said, time may clear away some of its incongruities. Meanwhile I have an experiment to propose." And leaning close to the Inspector, notwithstanding the fact that there was nobody within hearing and he knew it, he whispered a few words in his ear. The Inspector stared. "To-night?" he asked. The detective nodded. IX WHILE THE CITY SLEPT Night--the night of a great city with its myriad of garish lights and its many curious and incongruous activities. Who has not felt his imagination stirred by the contrasts thus offered--contrasts never more apparent than at these hours of supposed rest? Grim walls, with dimpled children sleeping behind them! Places of merrymaking athrob with music and dazzling with jets of incandescent light, with grief in the heart of the dancer and despair making raucous the enforced laugh! But nowhere in the great city of which we write on this night of May 23, 1913, was there to be found a scene of greater contradictions than in the court and galleries of its famous museum.