She halted her roadster at the very end of the pavement in such a position that the bright headlights played upon the massive walls of the Hamilton building.
"It must be located higher up," Penny murmured to herself.
"What is?" Susan demanded. "I don't see what you're about anyway."
Without answering, Penny directed the beam of her spotlight upon the stone structure. Inch by inch she moved it systematically over the high wall.
"Perhaps it's only a silly idea," she acknowledged at last, "but I believe that somewhere in the wall there must be a secret door—one mechanically operated. No doubt the outline of the opening is disguised by the many irregular cracks in the masonry."
"If you're looking for a secret opening, why not come in the daytime when you can see much better?"
"I've been here in the daytime and the door can't be detected—at least not by the eye. I'm hoping to have better luck this time."
"I can't for the life of me see how," Susan began, but ended with a startled gasp.
A portion of the massive wall was slowly moving backward.
"Just as I thought!" Penny chuckled in delight. "Now we know how Rap Molberg escaped from the police the other night."