Lydia and William Guthrie, with their cousin Molly, search for the most precious treasure of all. After a mysterious letter arrives with a treasure map, the Guthrie clan embark for adventure to find a mysterious island, only to learn a Band of Pirates is after the same treasure. Along the way, the Guthries discover more than treasure when the pirate Captain reveals a family secret that even the Guthrie children never before suspected.—T.L. Jones