If there's one thing Rosemary Rita can't resist, it's a mystery. Naturally, she's intrigued when she reads about a treasure map in a postcard her great-grandfather wrote to her grandmother Mimi in 1947. So, with a flip of the magic hourglass, back in time Rosemary Rita goes, and that's when things get really interesting! Her incredible journey leads to Green Turtle Cay Island in the Bahamas. There she helps ten-year-old Mimi and their new Bahamian friend, also a ten-year-old girl, unravel the clues on an ancient pirate's map. Buried treasure, it turns out, is on the very site that greedy landowners want to develop. Can the girls save the quaint island from becoming a fancy resort?