Bailey Fish's grandmother, Sugar, decides to open a used-book store in a little barn at the neighboring Keswick Inn. When Bailey and her friends, Noah and Fred Keswick, help Sugar unpack the cartons, they discover that several books contain clues to a mystery involving an unusual Florida shell (alphabet cone). While the kids try to decode the meaning, a stranger shows up to search for specific books before the Book Barn opens. Meanwhile, the Keswicks have surprises of their own with the arrival of rescue horses to live at the country inn near Lake Anna. Then, Bailey helps the boys' mother plan a special surprise for Sugar at the grand opening, but there are unexpected results. Finally the treasure is revealed and Bailey makes a choice.Nonfiction backmatter includes horses (rescue and those belonging to famous Americans), Sanibel shells and the Shell Museum. Glossary, Web sites, related reading and discussion questions.