"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 lier Brother. "And, by Jove, Grace, if the stirrups
