"No," replied Donald, "we're shadowing a man who is wanted by Gen. Funston. That's him," pointing; "keep your eye on him." "I thought you chaps had something on," laughed the soldier. "You can bet on me!" Now that they approached nearer the center of the business portion of the city, there were more people on the street; but they were so near their quarry that they easily kept him in sight. Only once had he glanced back, but that was enough to convince him that he was followed. "He's headed for somewhere," said Adrian. "He doesn't expect to get away from us simply by walking." "Right," agreed Donald. "There he goes into the post office." "Yes," from Adrian, "and it has two doors. You stop at the first one and I'll run to the other." He started on a run and the soldier followed suit. The sight of a man running and a soldier following, quickly attracted attention and pedestrians began to stop and see what the matter might be. In less than a minute a crowd had collected, among them several soldiers, who quickly brought Adrian to a halt. "What's the matter?" asked one. Then as the soldier came up: "What are you chasing him for?" "I'm not chasing him," laughed the seeming pursuer. "He and I are after another chap." The delay occasioned by this interference was not great, but it was sufficient to allow Strong to escape, had it not been for Donald. He had seen the crowd gathering and, realizing what would happen, ran around the other way, just in time to see Strong disappearing around the corner of the street on which the bank was located. Madly he dashed down the street and turned the corner in time to see Strong enter the big gate leading into the patio of Don Esteban's residence. Putting on more steam, a couple of minutes later Donald also dashed into the patio; but Strong was nowhere to be seen. "He must be in the bank," muttered the boy, and he quickly entered the door. But Strong had disappeared as completely as though the earth had opened and swallowed him up. CHAPTER XXX. THE MYSTERY SOLVED. When the opening at the head of the stairs had closed upon Billie and he realized that he was shut in a subterranean passage, for a minute his heart sank within him. He had tried to find an opening at the top of the opposite stairs and had failed, and he did not know that he would have any better success in trying to find a way to open the place through which he had descended. "Nobody on earth knows that I am down here," he thought, "and with Santiago sick and maybe dying, no one on earth probably knows that there is such a passage." But Billie was not the lad to sit down and cry. He had been in tight places before and he had an abiding faith in his own ability to do things. Therefore, he called up his courage and slowly mounted the stairs leading to Santiago's patio. At the top of the stairs he found himself confronted by exactly the same condition as he had found on the opposite side.