"What are you talking about, Bert?"
"Oh, nothing. I was just thinking."
"Well, don't think so loud unless you are going to take me into your confidence. Any chance of getting out of that dungeon cell of yours, Miss Juanita?"
"None."
At this moment they heard the sound of regular footsteps outside.
"'Sh," whispered the voice. "It is the guard. Go away from the window."
The boys jumped down from the table, and as they did so, Bert stumbled and fell heavily against the wall. When he recovered his balance they heard a strange grinding sound like a heavy door creaking on rusty hinges. The boys listened in wonder.
"Gee, but this is a creepy old place," said Bert, as the noise continued. "Now, what do you suppose that is?"
"It sounds as if it came from the wall there. Let's investigate."
They moved nervously over to the stone wall that separated their prison room from that of Miss Juanita. The noise seemed nearer and more distinct, but they could see nothing that might cause it. Still the strange sound continued. In the semi-darkness they watched in wonderment the blank face of the wall from which the sound seemed to proceed. Suddenly Harry seized Bert by the arm.