"I can't go much further!" gasped poor Bob. "My ankle pains me something awful!" "Don't ye be afther givin' up!" said Pat Stoodles. "We'll soon be at me castle, which all the savages on the island can't conquer." They were now passing along the bed of a small stream which flowed into the lake. Presently before them arose a beautiful waterfall, twenty feet high and eight or nine feet broad. "That's the dure av me castle," announced Stoodles. "Make a quick sthep inside an' ye'll not git overly wet." With this he dove straight into the waterfall and disappeared from view. "Gracious! What does that mean?" came from Dave. "He is mad and has committed suicide," muttered the doctor. "Perhaps not," came from Bob. "That waterfall may conceal the entrance to a cave." "Hurrah! I believe you are right," answered Dave. "And I am for finding out," and he took a step forward. But the captain caught the young diver by the shoulder. "Don't be rash, lad. It may cost you your life." Scarcely had Captain Broadbeam spoken when Stoodles reappeared through the falling sheet of water. "Come on!" he cried. "Don't be afraid. The futtin' is safe enough," and again he disappeared. None of the others hesitated any longer. Dave went first, holding his breath as he took the plunge. To his surprise the falling body of water was less than four inches thick, and in a moment he found himself on a smooth, rocky floor. "That's the greatest yet!" muttered Bob, when all were safe in the cave under the upper stream. "Don't the savages know of this?" he asked of the Irishman. "Sure not. Once they followed me up the strame an' I scared the wits out av thim, talkin' to thim from the wathers!" And Pat Stoodles laughed loudly, a laugh that echoed and re-echoed throughout the cavern. It was pitch-dark, but soon they had a light, and Stoodles brought forth a torch. Then he led the way to a branch of the cave, on higher ground. Here the flooring and walls were perfectly dry, and here the castaway had something of a comfortable home, with a rude table, a bench, a sea chest, and a cupboard with dishes and other household articles. In one corner of the cave was a rough fireplace, the smoke of a fire going up through half a dozen small cracks. It was easy to see that the castaway had not always been simple-minded. "I knew him years ago quite well," said Captain Broadbeam. "He once sailed under me. He is suffering for the want of companionship. Many a castaway, you know, has gone stark mad through loneliness. The savages were really no company for him." "Do you think he will get over it?" asked Dave. "I think he will," put in the doctor. "I have seen such cases before. Sometimes the recovery is quite rapid, when the castaway gets back among his own people." Leaving the crowd seated around a comfortable fire, in order to dry their clothing before going to sleep, Pat Stoodles returned to the entrance of the cave.