He started across the enclosure, picking his way carefully among the bushes. The long grass tripped him, but he persevered. Once he ran plump against something tall and hard, and after feeling it with his hand he knew just where he was, for it was the tombstone of Major Smith, who died in the fort of yellow fever in 1867, and was buried on the spot. That made his flesh creep just a little bit, but he kept on. After he reached the sally-port, which always stood wide open, he turned to the right, dodging piles of solid shot, a fallen partition, and an old steam-engine. In a minute more he was in front of the casemate he wanted--not the casemate which he had stood in so many times already to look out upon the sea, but a particularly gloomy one he remembered. He stepped into the casemate, about two feet higher than the ground, and the thick darkness staggered him for a moment. But he would not back out now. Slowly he groped his way across the stone floor. Crash! In a second he saw a thousand stars shooting, and like a flash he thought he realized that some one had struck him a blow on the head. "Help! help! help!" he shouted. "Murder! help! help!" He put up a hand to ward off a second blow, and found that it was dripping wet. Blood, perhaps! Something was trickling down his face. Maybe that was blood too! He was dripping all over. He tried to run, but he could not, for something held his feet. He was standing in water above his knees! Then he realized his terrible situation. Somebody had uncovered the trap in the casemate and left it open, and he had fallen into the tank. He was down in that horrible, black, slimy pit. Perhaps he had struck his head in falling, but the water had broken the fall. "Help! help!" he cried, when this dawned upon him. But he soon stopped that. All the men, he knew, were on the opposite side of the fort, and probably all in bed. There was not the faintest hope of making any one hear if he shouted all night. To climb out was impossible, for the hole was six feet above his head, in the middle of the ceiling. He was doomed to spend the night in that dreadful place, and in the morning he might hope to attract attention. How long he stood there, shivering with the damp chill and with terror, he does not know. It was long enough, at any rate, to make him fear that he might lose his senses before morning, and fall and be drowned in the slimy black water. Perhaps older fellows than Frank would have shivered with fear in that awful black vault. He had pulled himself together enough to try to dry his upper clothes, when he was startled by a slight noise overhead. Yes, he was sure he heard a noise; and the next moment he heard a voice. Ah! surely a human voice never sounded so sweet before! He had his mouth ready to cry out for help, when he caught a word or two that made him pause to listen. "I tell you I'll wait no longer," the voice said. "They're all in bed before this, and we're going to work. Come on."