"Hope they don't step off of there," the youth breathed, his heart in his mouth. At last, just as the sun was beginning to sink behind the distant peaks, the camels and their riders came to a stop at an opening in a mountainside that evidently led into a cave. Hardly able to hold the binoculars steady, Bob watched breathlessly, almost expecting to catch sight of Joe and Dr. Kirshner. But those individuals did not make an appearance. Bob did not doubt, however, that they were in the cave. A moment later, captors and captives dismounted from their dromedaries and walked through the opening out of sight. Bob waited silently for another half-hour, thinking that it might be possible that this was only a temporary prison. But when at the end of that time no one had left the cave, he was convinced that this was a permanent hideout. "Now I suppose it's up to me to get down from here right away," Bob thought, gliding silently off the shelf and onto a narrow ridge that was directly below. Carefully he felt his way down with great difficulty. As he had surmised, the descent would prove much harder than the ascent. Once his heart sank, as he saw that a five-foot wall of stone was directly below him. But then he suddenly remembered that a little to his right there were protruding rocks that would offer footholds. He edged around, and in a short time was again climbing steadily down. The minutes passed. When he was a third of the way to the bottom, darkness began to fall rapidly. He realized that he could not get to the base of the peak before pitch darkness would envelop him. "But I've got to keep going down," he told himself, frantically feeling his way among the rocks. For the past five minutes he had been getting drowsy, sleepy. The day's strain was beginning to tell on him. With an effort he kept himself awake. He knew the grim consequences if he should suddenly fall asleep while making the dangerous descent of the peak. He was half of the way down; now two thirds. But a few more hundred feet remained, and he braced himself and continued his slow, careful movement. "Not much more now," he observed, glancing down. "Ought to make it in a few more minutes." Long before, darkness had come upon him, making the frequent use of his small flashlight necessary. Even then it was a hard task. "Must be almost to the bottom," he thought, when another fifteen minutes had passed. He flashed the light downward and saw that fifty feet still remained. Again he bent his efforts upon the descent that was still before him, and in no time had covered most of the distance. But just when he prepared to use his flashlight, a small rock gave way from under his left foot. He tried vainly to catch hold of a sharp crag, and then felt himself falling! CHAPTER XXV Going for Help When Bob reached the ground, he was sore from numerous bruises, but to his great joy his legs and arms responded to his efforts to move them.