Eva Ibbotson's hugely entertaining The Star of Kazan is a timeless classic for readers young and old.
In 1896, in a pilgrim church in the Alps, an abandoned baby girl is found by a cook and a housemaid. They take her home, and Annika grows up in the servants' quarters of a house belonging to three eccentric Viennese professors. She is happy there, but dreams of the day when her real mother will come to find her. 
And sure enough, one day a glamorous stranger arrives at the door. After years of guilt and searching, Annika's mother has come to claim her daughter, who is in fact a Prussian aristocrat whose true home is a great castle. But at crumbling, spooky Spittal, Annika discovers that all is not as it seems in the lives of her new-found family . . .