The Hidden Clue — Margaret Sutton

""It is strange that she remembers a doll's name and not her own,"" Judy agrees when her friends ask about the little girl Judy and her FBI husband, Peter Dobbs, have taken into their home after the orphanage fire. The mystery deepens when the toy shop where Judy has seen the doll apparently disappears. At the library across the street the little girl, known only as Sister, puzzles Judy still further by insisting that the librarian is her mother. They both seem to know a strange character called Auntie Grumble, but is she real? And who are the mysterious men who made the doll walk and talk and sing? Can Judy and Peter be sheltering a kidnapped child? Somewhere, Judy is sure, there must be a hidden clue to the identity of Sister and her baby brother. How Judy finds it and follows it against the wishes of her father, Dr. Bolton, makes an unusual mystery story that will at first baffle and then delight readers.