"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 a.s.suming 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 sc.r.a.ps 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 Appearing in the darkest night.

That it should prove a horse to be, Most certainly amazes me."

"Good!" exclaimed Will, with a laugh. "You are progressing, Mr. Lagg."

A goodly supply of oats was placed in a box near the tent that evening, and then the boys and girls sat about the camp-fire and talked, while waiting for the time to retire. The boys were to make the attempt to capture Prince.

CHAPTER XXIV

THE GHOST CAUGHT

"When do you expect to hear about little Dodo?" asked Grace, as the girls sat together on a log in front of the fire, "like roosting chickens," Will was ungallant enough to remark.

"Almost any day now," replied Mollie. "They were to wait for the most favorable time for the operation, and the specialist, so mamma wrote, could not exactly fix on the day. But I am anxious to hear."

"I should think you would be. Poor little Dodo! I'd give anything to hear her say now 'Has oo dot any tandy? '"

"Don't," spoke Betty in a low tone to Grace, for she saw the tears in Mollie's eyes.

"It was the strangest thing how Stone and Kennedy should turn out to be the two chaps in the auto," remarked Will, to change the subject.

"And you have never let on that Grace was the girl on the horse?"

"Never," answered Amy. "Don't say after this that girls can't keep a secret."

Frank was to watch the first part of the night, to be relieved by Allen, and the latter by Will.

"For, from what the girls say, Prince has been in the habit of coming rather late," Will explained, "and he's more likely to let me catch him than if you fellows tried it. So I'll take last watch."

Frank's vigil was unrewarded, and when he awakened Allen, who sat up, sleepy-eyed, there was nothing to report. Allen found it hard work to keep awake, but managed to do so by drinking cold coffee.

"Anything doing, old man?" asked Will, as, yawning, he got on some of the clothes he had discarded, the more comfortably to lie down on the cot.

"Something came snooping around about an hour ago. At first I thought it was the horse, and went out to take a look. But it was only a fox, I guess, for it scampered away in the bushes. I hope you have better luck."

"So do I. Dad wants those papers the worst way. If I could get them for him I'd feel better, for I can't get over blaming myself that it was my fault they were lost. It was, because I shouldn't have sent Grace for them when I knew how important they were."

Allen went to his cot, and Will took up his vigil. For an hour he sat reading by a shaded lantern, so the light would not shine in the faces of his chums. Then, when he was beginning to nod, in spite of the attractions of the book, he heard a noise that brought him bolt upright in the chair.

"Something is coming!" he whispered. He stole to the edge of the board platform, and cautiously opened the flap of the tent. The box containing oats and sugar had been placed a little distance away, in plain view.

"That's Prince!" exclaimed Will, for in the moonlight he saw a white horse eating from the box. The "ghost" had arrived.

Will resolved to make the attempt alone. He stepped softly from the tent, and made his way toward the horse. He had on a pair of tennis shoes that made his footsteps practically noiseless. Fortunately, Prince, should it prove to be that animal, stood sideways to the tent, his head away from it, so that he did not see Will. The boy tried to ascertain if there was a saddle on the horse, but there was the shadow of a tree across the middle of his back, and it was impossible to say for sure.

Nearer and nearer stole Will. He thought he was going to have no trouble catching him, but when almost beside Prince, for Will was certain of the ident.i.ty now, he stepped on a twig, that broke with a snap.

With a snort Prince threw up his head and wheeled about. He saw Will, and leaped away.

"Prince, old fellow! Prince! don't you know me?" called the boy, and he gave a whistle that Prince always answered.

The horse retreated. Will held out some sugar he had ready for such an emergency.