“What is?” eagerly demanded Belle. “You are talking in riddles.”
“This whole affair is a riddle, girls!” exclaimed Cora. “But what Hazel said gave me an idea. That cement wall seems solid, but it can’t be. If it were no one could pass. So it must be made to look solid to deceive those not in the secret. Probably it is a balanced stone like the ones you read of in stories of the cave dwellers. Some of them closed the entrances to their caves by heavy rocks, set on pivots, turning when you pressed on a certain mechanism. There are counterweights, just as in a window, which makes the heaviest rock move easily. I’m sure that’s what is in the passage—a balanced rock doorway. And there won’t be any need of tearing the wall down at all!”
“It sounds like a detective story,” commented Bess.
“It may turn out to be one before we’re through,” Cora said.
“Oh, dear! Why don’t those boys hurry back?” cried Belle for perhaps the tenth time. “Let’s go out and look down the road to see if they are coming.”
The girls went out, too anxious and too eager to sit still, but they had no sight of Jack and his chums.
“I’m not going to wait any longer!” exclaimed Cora at length. “If I’m right, there will be no need of tearing down the wall. That is, if I can find the mechanism that turns the rocky door. And if I’m wrong, there won’t be any harm in doing it.”
“Doing what?” asked Bess.
“Going down into the passage to see what we can discover. Will you come?”
“I will!” exclaimed Hazel.