Slowly the youths moved up to the entrance and peeped around the corner. Satisfied that there was no one in sight, they went inside. "Nobody here but our dads and Dr. Kirshner," observed Bob, glancing about. "I wonder if they noticed the Arabs?" "Let's ask them." The men had noticed the fellows, they said, but thought nothing about it. Why? Was anything wrong? Bob explained that they were the two who had acted in a suspicious manner on the ship, and at once the scientists' faces lightened. "Come on," urged Dr. Kirshner. "We can't get there any too rapidly. When they find that we haven't got the map, they'll probably help themselves to money and anything else that happens to be lying about. They may even search other rooms." Hastily, and yet quietly, the boys and their elders went up the stairway. They were unarmed, their revolvers and other firearms having been left in their rooms. This might prove a handicap if the Arabs possessed weapons, but the Americans thought nothing of the risk they were taking. "We're five to two, even if we haven't our guns," said Bob, clinching his fists. "They're likely to be shaken by numbers." But Dr. Kirshner, who knew the ways of these cunning natives, smiled grimly. In a short time they reached the floor on which were their rooms and turned cautiously down the hall. With utmost care lest they be discovered, the explorers tiptoed up to their rooms. Mr. Holton took the lead and glanced around the door into the room. A moment later his face scowled. "What is it?" demanded Joe, in a whisper. "Are they inside?" Mr. Holton shook his head. "Worse than that," he said solemnly. "Take a look." While the others are taking in the situation, it might be well to tell something about Bob Holton and Joe Lewis and, incidentally, their fathers. Bob was a big, well-built youth of some eighteen years. He was particularly fond of adventure and life in the open, and always welcomed an opportunity that might bring about a realization of his desire. Joe, who was about the same age, was of medium size and strength, with a naturally dark complexion that was now still further darkened by the tropical sun. He, like his friend, was fond of adventure, hunting and fishing and hiking whenever the opportunity presented itself. The youths were together much of their time and agreed on practically every point. Their home was in Washington, D. C., where their fathers, Mr. Holton and Mr. Lewis, were employed as naturalists by a large museum.