The house with the dormer windows consisted, as has been previously mentioned, of four stories and an attic. Its roof rose several feet above the level of the window of Ruth's room, which was on the fourth floor of the apartment building. But Duvall saw at once that this elevation of the adjoining house did not extend all the way back, but, in fact, stopped a little beyond the point where it joined the apartment. From here to the rear of the lot the building had no attic, its rear extension being but four stories high. In this position on the apartment-house roof, the roof of the back building was at least fifteen feet below him. Another thing that he noticed at once was the fact that the second house, No. 162, was of almost the same design as the first, that is, it consisted of a main building with an attic, and a rear extension, reaching to the same level as that of the house between. It was clear that if anyone living in the second house could obtain access to the roof of the back building, he would be able to walk across that of the first or adjoining house, and reach a point directly beneath where he stood. But, granting the possibility of this, of what use would it be? A person on the roof below him would in no conceivable way be able to reach either of the windows of Ruth Morton's room. Was it possible that an opening had been made through the wall of the apartment building itself? He thought it unlikely, but determined to investigate. "I must get down on that roof below," he informed his companion. The janitor grinned. "How are you going to do it?" he asked. "Haven't you a ladder--a rope?" The man thought a moment. "I've got a short ladder in the cellar, only about eight feet long, I guess. I'm afraid it would not do." "Yes it would," replied Duvall, pointing to the roof of the attic portion of the house below. "I'll get down to the roof of the main part of the house first, and from there to the roof of the back building. An eight-foot ladder will be long enough for that. Bring it up, will you?" The man hesitated. "I don't just like this idea of going on other people's roofs," he said. "You don't need to go. I've got to. I'm a detective, and I'm working for Mrs. Morton on a most important case." As he spoke, he took a bill from his pocket and pressed it into the man's hand. The janitor responded at once. "I'll fetch it up, sir," he said. "Wait for me here." Duvall occupied the few moments consumed by the janitor's absence in examining, by means of his pocket electric torch, the surface of the roof on which he stood. The smooth flat terra cotta tiles showed no distinguishing marks. Here and there spots of paint, marred by footprints, indicated where the painters at work on the building had set their buckets, no doubt while painting the wooden portions of the trapdoor, and the metal chimney-pots on the roof.