“Girls! Fellows!” he cried. “Come here!” They all hastened to his side. He pointed to some marks in the sandy soil. “What are they?” he asked, excitedly. “Hoof marks!” cried Allen, dramatically. “That’s right!” agreed Will. “They are the marks of a horse! Girls, that’s what your ghost is—a white horse, and—and——” He ceased abruptly, looked at Grace strangely, and then brother and sister gasped together: “Prince!” “What?” demanded Allen. “I’ll wager almost anything that this ghost is my white horse, Prince, that has been missing so long!” went on Will. “But how in the world he could have gotten on this island, so far from the mainland, is a mystery!” “Couldn’t he swim?” asked Frank. “Of course!” cried Will. “I forgot about that. And Prince was once a circus horse, or at least in some show where he had to jump into a tank of water. Prince is a regular hippopotamus when it comes to water. Strange I never thought of that before! “But this solves the ghost mystery, girls. You and the other folks have been frightened by white Prince scooting about the island.” “We—we weren’t so very frightened,” spoke Mollie. “But the rattling chains?” questioned Grace. “What were they?” “The stirrups, of course,” answered her brother. “And, by Jove, Grace, if the stirrups are on Prince the saddle must be on him also, and the papers——” “Oh, isn’t this just fine!” cried Grace, her face alight. “Now papa can complete that business deal. I never loved a ghost before. Dear old Prince!” “Of course we are assuming a lot,” said Will. “It may not be Prince after all, but all signs point to it. He must have been on this island all the while. No wonder we could get no trace of him. Probably he was so frightened at the storm and the auto, and his fall, that he ran on until he came to the lake. Then his old training came back to him, and in he plunged. There’s enough fodder here for a dozen horses. He’s just been running wild. I’ll have my own troubles with him when I get him back.” “But how are you going to do it?” asked Frank. “We’ll search the island for him,” replied Will. “Come on, we’ll start now.” Changing from their bathing suits to more conventional garments, the boys and girls at once began a tour of the island. But though it was not very large, there were inaccessible places, and it must have been in one of these that Prince hid during the day, for they neither saw, nor heard anything of him. “We’ve got to set a trap!” exclaimed Will. “How?” asked Grace. “Well, evidently he’s been in the habit of coming around the tent to get scraps of food. We’ll leave plenty out to-night, and also some oats. Then we’ll watch, and when Prince comes I’ll catch him.” The boys voted this plan a good one. They went over to Mr. Lagg’s store in the _Gem_ to get a supply of fodder for the trap. “A horse on the island!” exclaimed Mr. Lagg. So that’s the ghost; eh? Well, it’s very likely, but it sort of spoils the story; “A ghostly ghost—a ghost in white