"When he returns," he said, "we can hide in here until he has gone out." Dr. Cairn nodded; he was peering about the room intently. "This is the place I came to, Rob!" he said softly; "but there was a stone stair leading down to some room underneath. We must find it." The old man could be heard passing from room to room above; then his uneven footsteps sounded on the stair again, and glancing at one another the two stepped into the cupboard, and pulled the door gently inward. A few moments later, the old caretaker--since such appeared to be his office--passed out, slamming the door behind him. At that, they emerged from their hiding-place and began to examine the apartment carefully. It was growing very dark now; indeed with the door shut, it was difficult to detect the outlines of the room. Suddenly a loud cry broke the perfect stillness, seeming to come from somewhere above. Robert Cairn started violently, grasping his father's arm, but the older man smiled. "You forget that there is a mosque almost opposite," he said. "That is the _mueddin_!" His son laughed shortly. "My nerves are not yet all that they might be," he explained, and bending low began to examine the pavement. "There must be a trap-door in the floor?" he continued. "Don't you think so?" His father nodded silently, and upon hands and knees also began to inspect the cracks and crannies between the various stones. In the right-hand corner furthest from the entrance, their quest was rewarded. A stone some three feet square moved slightly when pressure was applied to it, and gave up a sound of hollowness beneath the tread. Dust and litter covered the entire floor, but having cleared the top of this particular stone, a ring was discovered, lying flat in a circular groove cut to receive it. The blade of a penknife served to raise it from its resting place, and Dr. Cairn, standing astride across the trap, tugged at the ring, and, without great difficulty, raised the stone block from its place. A square hole was revealed. There were irregular stone steps leading down into the blackness. A piece of candle, stuck in a crude wooden holder, lay upon the topmost. Dr. Cairn, taking a box of matches from his pocket, very quickly lighted the candle, and with it held in his left hand began to descend. His head was not yet below the level of the upper apartment when he paused. "You have your revolver?" he said. Robert nodded grimly, and took his revolver from his pocket. A singular and most disagreeable smell was arising from the trap which they had opened; but ignoring this they descended, and presently stood side by side in a low cellar. Here the odour was almost insupportable; it had in it something menacing, something definitely repellent; and at the foot of the steps they stood hesitating.