“The rain will put out the forest fire,” concluded Tom. “Then we can get out of here and back home.”

“Home seems a long way off,” sighed Mary.

“We can make it pretty quickly by going down the brook,” suggested Tom. “The brook always rises a short time after even a little rain, for all the water in this section drains into it. I know where there’s a boat hidden in the bushes not far from here, and we can paddle down in that.”

“It sounds enticing,” returned Mary. “Oh, I look a fright, don’t I?” she asked, with a nervous giggle. Having been in the cave a little while, their eyes were more accustomed to the gloom and they could see better.

“You do not!” emphatically cried Tom, which, of course, was the right answer.

“It has been a wonderful experience,” she went on slowly. “Not that I would care to repeat it—Oh, Tom!”

She suddenly gave a gasp of fear and covered her eyes with her hands as a blinding flash of lightning seemed actually to shoot through the cavern. It was followed a second later by a crash of thunder which made even Tom Swift, used as he was to experimenting with big guns, jump.

“Here comes the rain!” he cried.

At that moment the storm broke with almost tropical fury, the big drops pelting down like hail on the burning trees, bushes and such dry leaves as had accumulated from the previous fall.

“This will douse the blaze,” went on the young inventor.