Spencer Vance sprung to his feet, and stood and listened, determined to have the drop on the other man in case of danger, and not again get caught in the position he was when the first smuggler called him to account. The intruder passed on his way without having come upon our hero and his gagged prisoner. The detective stole after the man, but concluded he was merely a resident of the island who passed by through chance. Returning to his man Vance made sure that he could not release himself, and then started down to the shore and moved along the beach, hoping to come upon the smugglers engaged in the unloading of their goods. The detective traversed about four miles of coast when, far ahead of him, he saw the glimmer of dancing lights. "Aha!" he muttered, "I've got 'em!" He spoke in an incautiously loud tone, when a man sprung toward him. The smugglers had put out sentinels, and our hero had run across one of them. The sentinel proved to be a resolute fellow, as he did not stop to ask questions, but made a stroke at the detective's head. Our hero dodged the blow, and seized the fellow; The man struggled violently, and made several attempts to sing out an alarm, but he was in a grip of iron. The detective, however, had no time to spare. He was an overmatch for the smuggler, but at any, moment assistance might arrive. It was silence the officer needed at that moment, and he buried the fellow's head under water. The poor fellow struggled violently, and it appeared a cruel recourse, but our hero knew that the water would render the man temporarily harmless. He did not mean to drown him. The man's struggles finally ceased, when the detective raised his head from the water. The fellow was not dead, but his cries were stopped for the time being--a water gag, as our hero termed it. Vance left the man lying on the beach, and advanced more cautiously. He had crossed the line and was in the charmed circle. Like an Indian on a trail he crawled forward, and, regardless of peril, approached quite close to the working party. Just above the water-line was a wall of rock, and built upon the rock was a small house, and into this house the goods were carried. The detective saw that the house was not of sufficient dimensions to hold all the goods that were carried in, and he made up his mind at the proper time to make a survey of the place and delve to the secret. Nothing more was to be done that night. He had ascertained all he desired. He had located the rendezvous and the store-house; while on the yacht he had marked some of the goods, so that he could identify them. He had trailed down the methods, noted the active workers, and all that remained was for him to get safely off the island and trace down to the backers. He had taken long chances, but all his risks were amply repaid by his wonderful success.