To a man of his nature it was the most pleasurable work in the world, studying the intricacies of a mystery, grasping a thread in the labyrinthine maze, following it along inch by inch, until the whole thing resolved itself into a solved problem. Then, when the end came, how proud he would be to survey his work. He began to give Joe the benefit of the doubt. This was one point gained. It is a rule in American courts never to adjudge a man guilty until he has been proven so—the law looks upon him as innocent, and all efforts of the prosecutor are directed toward proving the charges. In some other countries the opposite is the case and the accused has to prove his innocence. Eric Darrell was gradually applying this former principle to the case in question. Perhaps Joe might be innocent, and this cloud hanging over him be the result of circumstantial evidence. At any rate the detective hoped so. He looked at his watch mechanically. Just now the thought came into his head that he must find out all about Joe before another night had spread its mantle over the city. The time dragged along. He had some work to do in his office, and this consumed something like an hour. Then he made his way slowly in the direction of Twenty-seventh Street. It was about four when he came in sight of the house around which clustered so much that was mysterious. Sauntering along, he kept watch for Joe, feeling almost sure the other would come. Sure enough, at the regular time his tall figure came in view. Darrell managed it so that at this moment he was nearly opposite the house. He could see Joe without looking in a particular manner across the street, and he saw that the other appeared nervous and worried. Was his guilty secret wearing on his mind? Something undoubtedly disturbed him. Any one could see that from the expression on his face. As usual, when he came in front of the house, he turned and looked up the street, as though he were afraid lest some one whom he knew would recognize him. Then he went up the steps. There was no ringing the bell. With a key he opened the door as though proprietor there. Then Darrell, passing on, lost sight of him. The detective crossed the street beyond, and came on down, intending to pass the house again. He changed his mind. When just opposite, looking up he saw that fortune beckoned him. The door was ajar. Joe had been a trifle careless, and made a mistake when he thought he closed the door. What could be better? Mr. Darrell was a man quick to make up his mind, and he instantly saw a chance here to further his plans. Without hesitating an instant he advanced up the steps, stood upon the door-step, and seemed to glance around carelessly, when in reality he was listening to catch any sound that might come from the interior. Another moment and he had entered.