This book was 100% adorable, and if I had found it as a middle-grade reader, I would have loved it. There were aspects of it that were wholly unbelievable, and the portrayal of both Sherlock and Mycroft Holmes was not canon, but I am no purist and didn't care a whit.
The basic premise is that Sherlock & Mycroft's mother had a late in life child, Enola, who is 14 at the time that Sherlock is well into his career (it's post Hound of the Baskervilles, for sure). One day, her mother up and abandons her, leaving her notes (with money) hidden around the house. She decides that she is NOT going to a boarding school, and runs away, finding a kidnapped peer, and getting kidnapped herself, on her travels, all the while uncovering a charlatan who has been separating the gentry from their money under the pretenses of being a psychic.
This was a quick little read that I was able to check out from library using overdrive. I thoroughly enjoyed it, and if you have kids, especially girls, who like mysteries, this might be a good one to recommend. Bonus points if they enjoy the original Sherlock Holmes tales.