I am indebted to Colleen at http://www.chasingray.com/ for this as well as the Sisters Grimm… I think she wrote a column about mysteries for kids and teens last summer. Somehow I missed the first in the series and started with the second… though I made it through without noticing, you might wish to start with the first book, The Case of the Missing Marquess.
The Case of the Left-Handed Lady by Nancy Springer. Read by Katherine Kellgren. Enola is the much younger sister of Sherlock – just 14, and knowing her older brother mostly through Dr. Watson’s famous books. Her mother recently ran away, and Enola is now living on her own, hiding from her brothers, who want to send her to boarding school. She and her mother communicate via ciphers in the newspapers, which enterprising readers could try to solve for themselves. Enola is posing as the secretary to a Scientific Perditorian or finder of lost persons, intending to do the finding herself. Dr. Watson comes to her office, seeking help in finding her, but accidentally leading her to the case of a missing society lady, only a few years older than herself. The police and Sherlock Holmes assume that she’s eloped, but Enola doesn’t believe it and uses her wits and multiple disguises to solve the mystery. Enola is an excellent character, determined to stay independent but still figuring herself out, and ever conscious that her name, backwards, spells “Alone.” Raised feminist by her mother, she knowingly manipulates the Victorian conventions regarding females to fit in multiple places without resorting so low as to disguise herself as a man, from high society houses to London’s poor and sooty underbelly. My husband and I both very much enjoyed these. For the children it’s actually aimed at, parents should be aware that there is some violence that could be disturbing for younger or sensitive children – I’d put it as more appropriate for 12 and up than the 10 years I read on the case. Katherine Kellgren’s assured British accents are perfect for Enola and adapt themselves well to the many characters of different classes in the book. Enola might not exist without Sherlock, but she’s well worth reading in her own right, a strong character in a vivid (if vivid is the right word for sooty fog) setting with just the right balance between plot tension and introspection.