"Well, Dowd, as soon as Skinner began antagonizing our moves, I suspected that he was the writer of the letter of warning. Then I ordered his history--you know those things are easily obtained. He came here years ago it seems, comparatively unknown, and worked his way up, employing a young fellow for many years in his office. This young fellow went West, but returned later. He was Maloney. He had not the mental attainments for his employer's business, but the older man kept in touch with the younger, even after he found it necessary to dispense with his services. When I saw Skinner, I detected some resemblance between them--this seems to have escaped general notice, but Dr. Moore was not deceived. A study of the eyes and the ears and the nose confirmed my suspicions of the paternity of Maloney; but all that, while interesting, was not so valuable as the knowledge that Maloney had several handkerchiefs given him by Skinner. You see, Skinner's conduct was so suspicious throughout that we have investigated him thoroughly. We found he wore such handkerchiefs around his neck in the printing office. We found Mrs. Cook was aware that Maloney had some of them--he told her that Mr. Skinner gave them to him. He always was proud of Skinner's friendship." "Then you knew all about it this morning, Quintus," I cried, exasperated at the man's taciturnity; "you knew when you said you would tell who O'Brien was, if I would tell whether the 'S' had anything to do with Skinner." "No, but I mistrusted; the proofs were only more recently secured." "Then, as you now have the answer regarding the 'S,' it seems only fair that you tell us who O'Brien is," I cried. Oakes became very serious. "I believe O'Brien was the man watching on the balcony when Dr. Moore was assaulted; also that he was the man at the bridge who warned you, Stone, of danger, but who has kept his identity hidden. We had strong proof that he was at the hut watching, as were we; he accidentally left a part of his shirt with my man, remember. I also believe that he was wounded and is in hiding--wounded by Maloney, on the Highway, when he was about to close in upon him." "What do you mean?" cried Moore. "What curious conduct for a man--to keep in hiding!" "No, not at all," answered Oakes sharply. "Remember how you saw him on horseback one night, revolver in hand. Well, he was attending to business. _O'Brien is working on the Mansion mysteries._ I believe he only knows half of the affair; he does not realize Maloney may be the murderer of Mark--his conduct is in accord with that of a brave detective working single-handed and desiring to keep his identity secret." "A _detective_!" "Yes, I fancy so," answered Oakes, with a smile on his face. "Why not? We are not the only bees around the honeysuckle." "By George! I never thought of that," exclaimed Moore. "Indeed!" retorted Oakes in dulcet tones. "Why should you? You have not played this game before--it is new to you."