This is a vintage 1961 edition of The Hardy Boys, A Figure in Hiding by Franklin Dixon, volume 16. The antique hardcover book has a 1937 copyright by Grosset & Dunlap. Dating the various editions of the Hardy Boys series is a challenge and I dated this one using the websites below. The book has 212 pages, marking it as the 1937-1964 Leslie McFarlane (original ghostwriter) with Paul Laune art version while the brown multi-scene endpapers narrows the date to 1959-1961. Final pinpoint is the list of available books on the rear cover with "Mystery of the Desert Giant" (published in 1961) as the last book. This book was given to me in the 1960s by the original owner so that date fits as well. The book is in fair condition with lots of wear, especially around edges and corners. There are tears in the upper and lower bindings. The inside cover endpapers have tape on them and the binding has separated and needs to be reglued. (See photos) All of the pages are in place and clean.
http://hardyboys.us/hbos.htm#06
https://hardyboys.us/hbt16.htm