The Secret Of The Caves by Franklin W. Dixon

Two teenage sleuths investigate a young woman’s disappearance that leads them to a rugged coastline riddled with mysterious caves, where eerie signals and strange happenings suggest a hidden operation. Navigating treacherous passages and confronting a reclusive hermit, they piece together clues that reveal saboteurs using the caverns as a base. With quick thinking and teamwork, they rescue the missing person and dismantle the threat lurking beneath the cliffs.

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