A Time For Every Purpose Under Heaven — Barbara Hambly

A short story of 8,699 words, in the Benjamin January Free Man of Color series. Rose Janvier, Benjamin's wife, is left at home in pre-Civil-War New Orleans when Benjamin goes off to solve a crime in another city. When the high-living brother of one of her neighbors is murdered, Rose uses her own detective skills to track down the killer, despite the fact that the white City Guards have arrested her and everyone else on the street as suspects.