Secret of the Caves

The Hardy boys were sons of a celebrated American detective and from their father learned the particulars of a number of unusual crimes. They were fired with zeal to bring the criminals to justice, and during their hours from school, and during their vacation days, they followed up clues they unearthed themselves — aiding their parent very materially. Stories which are absorbing in the extreme. - Summary from the book jacket This is number seven of the "Original Ten" Hardy Boys books which have