While the two children sat in the drifting rowboat, which was being slowly blown toward the island shore again, Flossie suddenly gave a little jump, which made the boat shake.

"What's the matter?" asked Freddie. "Did something bite you?" for his sister had started, just as you might do if a fly or a mosquito suddenly nipped your leg.

"No, nothing bit me," she answered. "But I felt a splash of rain on my nose and—— Oh, Freddie! Look! It's going to be a thunder-lightning storm!"

Freddie, whose eyes had seen nothing but the cave, now looked up at the sky. The blue had become covered with dark clouds, and in the west there was a dull rumble.

"I—I guess it is going to rain," said Freddie slowly.

"I know it is!" Flossie answered. "There's 'nother drop!"

"I felt one, too," said her brother. "It went right in my eye, too!" and he winked and blinked.

"And there's another one on my nose!" cried Flossie. "Oh, Freddie! What are we going to do? I haven't an umbrella!"

For a moment the little boy did not know what to do. He looked at his coat, but that was still wet, though it had been spread out on the seat to dry. He could not wrap that around Flossie, as he thought at first he might.

The wind, too, was blowing harder now, and there were little waves splashing against the side of the boat. But the wind did one good thing for the children—it blew the boat toward shore so much faster, and shore was where they wanted to be just now. They knew they had drifted out too far, and they were beginning to be afraid. The shore of the island looked very safe and comfortable.

"We can get under a tree—that will be an umbrella for us," said Flossie. "Aren't you glad we're going on shore, Freddie?"

"Yes, but I guess we can get in a better place out of the rain than under a tree, Flossie."

"Then we'd better get," she said, "'cause it's rainin' hard now. I've got about ten splashes on my nose."

The big drops were beginning to fall faster. The clouds had quickly spread over the sky, which was now very dark, and the wind kept on blowing.

"Where can we go out of the storm?" asked the little girl.

"Huh?"

"Where we goin', Freddie?"

"In there," answered her brother, pointing.

"What! In that dark hole?"

"It isn't a hole—it's a cave. An' maybe we'll find gold and diamonds in there, like in the book Momsie read to us. Come on. We can go into the cave, and we won't get wet at all. I'll take care of you."

"I—I'm not afraid," said Flossie slowly. "But I wish Snap was with us; or Whisker. I guess Whisker would like a cave."

"So would Snap," said Freddie. "But we can't get 'em now, so we've got to go in ourselves. Come on. And look out, 'cause the boat's goin' to bump."

And bump the boat did, a second later, against the shore of the island, close to the open mouth of the black cave. It was raining hard now, and Freddie helped Flossie out of the boat, and then, holding each other by the hand, the children ran toward the cavern. No matter what was in it, there they would be sheltered from the rain they thought.

The cave, as Freddie and Flossie saw, could be entered from either the land or the water. At one side it was so low that a boat could be rowed into it for a little way. On the other one could walk into it by a little path that led through the trees. The water of the lake splashed into the cave a short distance, and then came to an end, making a sort of little bay, or cove, large enough for two or three boats. And the cave, as the children could see when their eyes became used to the darkness, was quite a large one.

"I wonder if anybody lives here," whispered Flossie, as she kept close to her brother.

"We live here now," he said. "Anyhow, we're going to stay here till the rain stops."

"Maybe a bear lives here," said Flossie in a whisper.

"Pooh!" laughed Freddie. "There are no bears on Blueberry Island, or daddy would have brought a gun. And he said I didn't even need my popgun, 'cause there wasn't a thing here to shoot. But I did bring my popgun."

"You haven't got it here now, though," said Flossie.

"I know I haven't. I left it in the tent by the go-around bugs. I mean before the go-around bugs got away. But my popgun is there. I saw it. Only I haven't it now, so I can't shoot anything. But there's nothing to shoot, anyhow." Freddie added the last for fear his sister might be frightened in the dark cave.

It was very dark, especially back in the end, where Flossie and Freddie could see nothing. But by looking toward the place where they had come in, they could see daylight and the lake, which was now quite rough on account of the wind. They could also see the rain falling and splashing.

"I'm glad we're in here," said Flossie. "It's better than an umbrella."

"Lots better," agreed Freddie. "If we had some cookies to eat we could stay here a long time, and live here."

"We couldn't sleep, 'cause we haven't any beds," declared Flossie.

"We could make beds of dried grass the way Bert told us to do if we went camping."

"But have you any more cookies?" asked Flossie, going back to what her brother had first spoken of. "I'm hungry!"

"Only some crumbs," Freddie said, as he put his hand in the pockets of his coat, "and they're all soft and wet. We can't eat 'em."

"Well, we can go home when it stops raining," said Flossie, "an' Dinah'll give us lots to eat."

The two children were not frightened now. They stood in the cave, and looked out at the storm. It was raining harder than ever, and the thunder seemed to shake the big hole in the ground, while the lightning flashes lighted up the cave so Freddie and Flossie could look farther back into it.

But they could not see much, and if there was any one or anything in the cave besides themselves, they did not know it. They saw the boat blown inside the cave, and it came to rest in the little cove, which was a sort of harbor.

Then, almost as quickly as it had started, the storm stopped. The wind ceased blowing, the rain no longer fell, the thunder rumbled no more and the lightning died out. For a few minutes longer Flossie and Freddie stayed in the cave, and then, as they were about to go out, the little girl grasped her brother by the arm and cried:

"Hark! Did you hear that?"

"What?" asked Freddie.

"A noise, like something growling!"

Freddie looked back over his shoulder into the dark part of the cave. Then, speaking as boldly as possible, he answered:

"I didn't hear it. Anyhow, I guess it was the wind. Come on, we'll go home!"

"Are we going back in the boat?" Flossie asked.

"I guess not," Freddie replied. "It'll be rough out on the lake—it always is after a storm. We can walk down the path to our camp. Besides, this isn't our boat. Maybe it belongs here and we'd better leave it."

"Then you'd better tie it," said Flossie. She and her brother had been told something of the care of boats, and one rule their father had given them was always to tie a boat when they got out of it. In the excitement of the storm the children had forgotten this at first, but now Flossie remembered it.

"Yes, I'll tie the boat," Freddie said, "and then whoever owns it can come and get it."

It did not take him long to scramble around to the edge of the little cove. Once there, he tied the rope of the boat fast to a large stone that was half buried in the ground. Making sure it would not slip off, Freddie came back to where Flossie waited for him.

She was quite ready to leave the cave, and soon the two children were outside under the trees that still were dripping with rain.

The sun was now shining. Flossie and Freddie had had an adventure, they thought, and that was fun for them.

"Which way is home—I mean where our camp is?" asked Flossie, as she and Freddie walked along together.

"Down this way," he said. "See the path?"

Certainly there was a path leading away from the cave, but Freddie did not stop to think it might lead somewhere else than to Twin Camp. It was a nice, smooth path, though, and he and Flossie set out along it not at all worried.

"I'm hungry," said the little girl, "and I want to get home as soon as I can."

"I'm hungry, too," Freddie said. "We'll soon be home."

But the children might not have reached the camp soon, only that a little later they heard their names called in the wood, and, answering, they found Nan and Bert looking for them in the goat wagon drawn by Whisker.

"Where in the world have you been?" asked Bert of his little brother and sister.

"Oh," answered Freddie, "we've been out in a boat and in a cave and we only had cookies to eat and they were wet and——"

"We heard a noise in the cave. Maybe it's a bear, an' if it is Freddie can take his popgun the next time we go there. Can't you, Freddie?"

"Dear me!" laughed Nan. "What's it all about?"

Then the two small twins told more slowly what had happened to them, and Nan and Bert told their small brother and sister that, coming back from their little trip, they had found Mrs. Bobbsey much worried because she could not find Flossie and Freddie.

"Then it began to rain," said Nan, "and we were all as worried as could be. We looked at our boats, and when we found they were tied at the dock we didn't think you were out on the water. Then when it stopped raining Bert and I started out to find you and so did Sam, though he went a different way."

"And we called and called to you," said Bert. "Didn't you hear us shouting?"

"Maybe that was the noise we heard in the cave," said Freddie to his sister.

"What about this cave?" asked Bert. "Tell us where it is."

Then, riding back to camp in the goat wagon, the two small twins told again of the big hole in which they had taken refuge from the storm.

"I'd like to see that," Bert said. "We'll go there to-morrow."

"We can walk there, or Whisker can take us," said Freddie. "And then we can come home in the boat, but you'll have to take some oars, Bert."

"That's so—there is a boat!" exclaimed the older Bobbsey boy. "I wonder whose it can be?"

But they did not learn at once, for the next day, when they all went to the cave—including Mr. and Mrs. Bobbsey—the boat was not there.

"Somebody untied it and took it away," said Freddie, as he pointed out the rock to which he had made fast the rope.

"Are you sure you tied it tightly?" asked his father.

"Yep. I made the same kind of knot you showed me," and Freddie told how he had done it. Flossie, too, was sure her brother had fastened the boat properly.

"Well, then somebody's been here in the cave," said Bert. "Say, it's a big place, Daddy! Can't we get a lantern and see where it goes to back there," and he motioned to the dark part.

"Some time, maybe, but not now," said Mr. Bobbsey, who, with his wife, had walked along the island path to the cave while the children rode in the goat wagon. "I didn't know there was a cave on Blueberry Island. I don't believe many persons know it is here. But the boat might belong to some of the berry pickers, and they hunted for it until they found it."

"Did the blueberry pickers make the funny noise in the cave?" asked Flossie.

"I don't know," replied her father. "I don't hear any noise now. I presume it was only the wind."

Mr. Bobbsey and Bert, lighting matches, went a short way back into the cave, but they could see very little, and the children's father said they would look again some other day.

"But, Flossie and Freddie, you mustn't come here alone again," said Mr. Bobbsey.

"If it rains and we're near here can't we come in if we haven't an umbrella?" asked Freddie.

"Well, yes, perhaps if it rains. But you mustn't go out in a drifting boat again, rain or no rain," ordered Mr. Bobbsey.

Flossie and Freddie promised they would not, as they always did, and then the camping family started back for their tents.

"What do you think of that cave, the boat's being taken and all that's happened?" asked Mrs. Bobbsey in a whisper of her husband, as they walked toward camp together.

"I don't know what to think," he said slowly.

"Do you suppose the gypsies could be in there?"

"Well, they might. But don't let the children know. They are having a good time here and there's no need, as yet, to frighten them."

For the next few days there were happy times in Twin Camp. The children went on many rides in the goat wagon and had other fun. Then, one afternoon when they were all sitting near the tents waiting for Dinah to get dinner, they saw a steamer heading toward the little dock.

"Oh, maybe it's company!" cried Flossie, clapping her hands.

And so it proved, for when the boat landed Mrs. Porter and her little girl, Helen, got off.

"We came to see how you were," said Mrs. Porter. "Helen wanted a trip on the water, so we came on the excursion boat. We're going back this evening. How are you?"

"Very well, indeed," said Mrs. Bobbsey, "and glad to see you. Helen can play with Flossie and Freddie."

"Did you see any of the gypsies, and did they have my talking doll?" asked Helen as soon as she had taken off her hat in the tent and had gone outside to play with the two small Bobbsey twins.