The Secret Gold of Blackwheat Manor by Gloria August

Mystery has come to Roseberry Topping, a quiet town on Edwardian England’s North Coast. Olive and Violet Bright, Jack Pems and Judith Pinckney, young sleuths and amateur detectives, have stumbled upon the punctilious town librarian, and her two companions. The three have been holding mysterious meetings in an abandoned manor house known as Mockery Gables, and the Bright sisters are convinced they’re up to no good. Soon, Blackwheat Jam, previously known only as a delicious spread for warm toast on cold mornings, has bubbled to life with a secret kept hidden for centuries. The sleuths take off on a wild ride across the English countryside as they pursue the three conspirators and their powerful secret. Hold the ponies and buckle up! The Bright sisters and their friends are about to shake the Holly District to the ground in a most extraordinary way!