Riddle of the Black Unicorn

Why would anyone strangle a humble seamstress with no known enemies? Newly-married bookseller Victor Legris is initially baffled by the murder of seemingly-unremarkable Louise Fontaine, in the abattoir district of La Villette. But as the investigation progresses, Victor, along with his assistant and brother-in-law Joseph, discovers that in belle-epoque Paris young girls with no money or background are as ruthlessly preyed on as ever...