The Case of the Left-Handed Lady by Nancy Springer

Enola Holmes is hiding from the world’s most famous detective—her own brother, Sherlock Holmes. But when she discovers a hidden cache of bold, brilliant charcoal drawings, she can’t help but venture out to find who drew them: young Lady Cecily, who has disappeared from her bedroom without a trace. Braving midnight streets where murderers roam, Enola must unravel the clues—a leaning ladder, a shifty-eyed sales clerk, political pamphlets—but in order to save Lady Cecily from a powerful villain, Enola risks revealing more than she should…