I sat spellbound as these men discussed the intricacies of the affair, realizing the truth of their reasonings and marvelling at the clues, conceptions and brilliant memories revealed, especially by the masterly Oakes. "Too bad you cannot find Skinner, and see what he is up to," I remarked. "We must let Hallen keep watch on him until we are ready for our final move. It would be easy to arrest him on suspicion, but that might defeat our object, and, again, I do not believe in making arrests until my case is clear," said Oakes. "Do you not think Skinner might be the murderer?" I asked. "Not as I see things now. It seems more probable that he is interested in someone whom he wants to get out of harm's way. His motive throughout this affair has been to hide the guilty, I think." "And what do you make of that man O'Brien?" queried Dowd; "he seems to be a mysterious fellow." Oakes and Hallen exchanged knowing glances. "He's another possibility; he's a little Tartar," said the detective. "But won't Maloney get away now?" asked Elliott. "Nit," was the answer from Hallen. "Those two 'laborers' with him are my 'specials.'" I was getting entirely tied up now, but, desiring to appear erudite and worthy of such company, I blurted forth: "Who is Mike O'Brien, anyway?" Oakes looked at us all coolly and exasperatingly. "He seems to be a little extra thrown in. I'll tell you all about it when you tell me if the 'S' on the handkerchief has anything to do with Mr. Skinner." An exclamation of surprise went up. We had all forgotten _that_. But before we could resume, a message arrived for Oakes. It was brought by one of the men whom we knew so well by sight around the Mansion. He told of the finding of a burned tree, hidden in the forest, near the scene of the murder of Mr. Mark. Those who were searching had discovered that the tree was recently struck by lightning and that within its burned interior was ash. The man had brought some with him, and also a small, crumpled piece of newspaper. Oakes looked carefully at them as we glanced over his shoulder. "At last!" cried he. "Here is wood ash--wet, as was that on the robe; and here is paper like that of the 'Daily News,' which we found in the robe; is it not?" "Yes," cried Moore. "It is indeed--can it be?" "Yes," came the answer from Oakes; "my orders to search for the origin of the ash have been crowned with success. The robe was in that tree." "But," I cried, "of what value is that?" "Just this--the robe was not worn at the time of the murder. Remember, Joe did not see it--it had been hidden, probably. The murderer used it to go and to come in, but for some unknown reason discarded it at the shooting." "Excuse me," said the messenger, "excuse me, Mr. Oakes--but that's about right. The tree was beyond the stone where he crossed and lost the handkerchief. He was running for the robe, sir; the murderer was after his disguise."