"Look out, Freddie! Don't you go wadin' too far!" cried Flossie, as she saw her little brother kick off his low shoes, quickly roll off his stockings, and start out toward the boat which now a strong puff of wind had blown quite close to the island shore.

"I'll be careful," he answered. "Mother said I could wade up as far as the wig-wag cut on my leg, and I'm not there yet."

Freddie had several scars and scratches on his legs, reminders of accidents he had suffered at different times. One scar was from a cut which he had got when he had fallen over the lawn mower about a year before. It was the biggest cut of all, and was near his right knee. He called it his "wig-wag" cut, because it was a sort of wavy scar, and when he wanted to go in wading his mother always told him never to go in water that would come above that cut, else he would get his knickerbockers wet.

So now he was careful not to go out too far. He watched the water rising slowly up on his bare legs as he waded along on the sandy bottom of the lake toward the drifting boat.

"If you took a stick you could reach it now," called Flossie.

"I guess I could," Freddie said.

"I'll hand you a stick," Flossie offered, looking for one along the shore. There were many dead branches, blown from the trees, and she soon handed Freddie a long one. With it the little boy was able slowly to pull the boat toward him, and he had soon shoved the "nose," as he sometimes called the bow, against the bank of the island.

"Now I can get in!" laughed Flossie. "And I won't have to take off my shoes and stockings either," and into the boat she scrambled.

"Oh!" exclaimed Freddie. "Are you going to get in the boat?"

"I am in," answered his sister. "Aren't you comin' in, too?"

Freddie looked at the boat, at his sister, at the lake, and at his shoes and stockings on the shore. Then he said:

"Well, it doesn't belong to us—this boat don't."

"I know," said Flossie. "But you pulled it to shore and we can keep it till somebody comes for it. And we can make-believe have a ride in it. Momsie won't care as long as it's fast to the shore. Come on, Freddie!"

It seemed all right to Freddie when Flossie said this, especially as the boat was close against the shore. He put on his shoes and stockings, drying his feet in the grass, and then he took his seat in the boat beside his little sister.

"Now we'll play going on a long voyage," she said. "We'll take a trip to New York and maybe we'll be shipwrecked."

"Like Tommy Todd's father," added Freddie.

"Yep. Just like him," said Flossie, "only make-believe, of course."

"And I'll be captain of the ship, and you can be a sailor," went on Freddie. "It'll be lots of fun!"

Bert and Nan had gone riding in the goat wagon to the other end of the island, Mr. Bobbsey was at his office and Mrs. Bobbsey, with Dinah, was working about Twin Camp, so there was no one to watch Flossie and Freddie. Mrs. Bobbsey supposed they were playing safely at the lake shore, and, as a matter of fact, they were on shore, though in the boat.

"I wonder whose it is?" said Freddie, when they had made a make-believe voyage safely to New York, after having been shipwrecked at Philadelphia—a place the little twins remembered, as one of their aunts lived in that city.

"Maybe it's a gypsy boat," said Freddie.

"Or else it's the one the blueberry boy had," added his sister.

"Oh, yes, maybe it is his!" cried Freddie. "And if it is, didn't we better ought to take it to him?"

"How?" asked Flossie.

"Why, we can push it along the shore with sticks, 'cause there's no oars in it, and when we see him picking blueberries we can holler to him to come an' get his boat."

Flossie thought this over a few seconds. Then she said:

"Let's!"

This meant she would do as Freddie said. The twins did not stop to consider whether they were doing something they ought not to do. They planned to keep near shore, and that was as much as they remembered of what their mother had told them—that they were not to go out on the lake in any boat without her permission or their father's.

"But paddling along the shore isn't going out," said Freddie. "Anyhow, mother and father would want us to give back the boat to the blueberry boy, wouldn't they?"

"Course," said Flossie. "Get another stick, Freddie, and we can poke the boat along, and we won't have to go far out at all."

In a little while the two twins were shoving the drifted boat along the shore by pushing the ends of their sticks into the soft bank. The boat was of good size, and it was flat-bottomed, which meant it would not easily tip over. Flossie and Freddie each knew how to row, though they had to have oars made especially for them. But they knew how to keep in the middle of a boat, and never thought of rocking it or changing seats, so they were much safer than most children of their age would have been.

Having lived near Lake Metoka all their lives, they knew more about boats and water than perhaps some of you small boys and girls do; and they could both swim, though, of course not very far, nor were they allowed to try it in deep water.

"Oh, this is lots of fun!" cried Flossie, as she and Freddie poled the boat along. "This is real trav'lin'!"

"But we mustn't go too far," said Freddie, not quite sure whether or not his mother would think what he and his sister were doing was just right. "As soon as we see the blueberry boy we must give him his boat and go back home."

"If he wants to row us back, can't we let him?" asked Flossie.

"Yes, but he can't row, 'cause there are no oars in the boat," said Freddie.

"Maybe he has 'em with him. I guess that's what happened," went on the little girl. "You know we take the oars out of our boat and put them up on shore. And then maybe the blueberry boy forgot to tie his boat."

"And it blew away and we found it," finished Freddie. "Come on, push hard, Flossie. Let's go fast and make believe we're a steamboat."

That suited Flossie, and they were soon pushing the boat along the shore quite fast. They went out past a little point on the island, some distance away from their own camp, the white tents of which they could see.

"Oh, how nice the wind is blowing!" cried Flossie, after a bit. "I don't hardly have to push at all, Freddie."

"That's good," he said. "We'll be a sailboat instead of a steamboat. If we only had a sail now!"

"Maybe you could hold up your coat," suggested his sister. "Don't you remember that shipwreck story mother read us. The men in the boat held up a blanket for a sail. We haven't any blanket, but if you held one end of your coat and I held the other it would be a sail."

"We'll do it!" cried Freddie, as he slipped off his jacket. It was small, but when he and his sister held it crosswise of the boat, the wind, which had begun to blow harder, sent the boat along faster than the children had been pushing it.

"Oh, this is fine!" Freddie cried. "I'm glad we played this game, Flossie."

"So'm I. But look how far out we are, Freddie!" Flossie suddenly cried. "We can't reach shore with our sticks."

Freddie looked and saw that this was so.

"I wonder if we can touch bottom out here," he said. "I'm going to try."

He let go of his coat, and as it happened that Flossie did the same thing, the little jacket was blown into the water.

"Oh!" cried Flossie. "Oh! Oh!"

"I can get it!" excitedly shouted Freddie. "I'll reach it with my pushing stick."

He managed to do this, taking care not to lean too far over the edge so the boat would not tip. Then he caught the coat on the end of the stick and pulled his jacket into the boat.

"Oh, it's all wet!" cried Flossie.

Freddie did not stop to tell her that every time anything fell into the water it got wet. Instead, he began to search in his pockets.

"What's the matter—did you lose something?" asked Flossie.

"I guess we can eat 'em after they dry out," said Freddie, after a bit, pulling out some soaked sugar cookies.

Freddie spread them out on one of the boat-seats where the sun would dry them, and then he wrung from his coat as much water as he could. Next he spread the jacket out to dry, Flossie helping him.

All this time the children failed to notice where they were going, but when they had seen that the soaked cookies were getting dry and had eaten them, Freddie looked about and, pointing to shore, cried:

"Oh, look, Flossie!"

"We're going right toward a big, dark hole!" said the little girl.

"That isn't a hole—it's a cave," Freddie said. "Maybe it's a pirate cave, and there'll be gold and jewels in it. The wind is blowing us and our boat right into it!"

And that was what was happening. The wind had changed, and, instead of blowing the boat away from the island, was blowing it toward it. And directly in front of Flossie and Freddie was a big hole in the steep bank of the island shore. As Freddie had said, it was a cave. What was in it?