De verdwenen professor

Blurb

The Secret of the Caves is Volume 7 in the original The Hardy Boys Mystery Stories published by Grosset & Dunlap.
This book was written for the Stratemeyer Syndicate by Leslie McFarlane in 1929. Between 1959 and 1973 the first 38 volumes of this series were systematically revised as part of a project directed by Harriet Adams, Edward Stratemeyer's daughter. The original version of this book was rewritten in 1965 by Andrew E. Svenson resulting in two different stories with the same title.