The Key in the Wall Mystery

Amateur sleuths Poppy and Sadie discover a key hidden in Aendi Hannah's guesthouse. Who hid the key, and why? Their crazy quilt clues-70-year-old letters promising a great treasure, a time capsule, and secret room-lay out no real pattern or direction. Will Sadie and Poppy's snoopery find the treasure? Or is the treasure lost forever?