Nancy Springer's The Case of the Missing Marquess
, the first book in her Enola Holmes mystery series for young readers.
Enola is Sherlock Holmes' sister -- and twenty years his junior. On her fourteenth birthday, her mother, sixty-four years old, vanishes from the family's ancestral estate. Enola informs her brothers in London, Mycroft and Sherlock, and they travel to the estate they haven't seen in a decade to unravel the mystery.
Then Enola discovers that Sherlock has atrocious interpersonal skills and Mycroft has plans for her, so she decides that she's going to make a run for it and solve the mystery herself.
Some of my enjoyment comes from knowing who Sherlock and Mycroft are from thirty years of reading (and even writing) Sherlock Holmes stories. Enola, even though she's their sister, doesn't have that benefit. To her, they are nothing more than strangers who share some history and a name.
Yes, it's a book for the junior high school crowd. Nonetheless, if you like Sherlock Holmes and plucky heroines, it's a hugely enjoyable book.