Notorious - The Vespertine Mysteries, #1

Raised in the wilderness of Buena Vista, Vespertine is still adjusting to living over her uncle's book store in gold rush San Francisco. When her employer coerces her into proving a fallen woman innocent of an infamous murder, she finds herself embroiled in a secret war between slavers and abolitionists. Vespertine is desperate to preserve her employment, maintain her standing with amiably corrupt Sergeant Cuinn, and save a woman from the gallows.
All before Tuesday.