The Black Tower

Louis Baynard.  Another great historical mystery from Baynard.  He also wrote Mr. Timothy (the story of a grown up Tiny Tim) and the Palest Blue Eye, both of which I recommend. Black Tower is about Vidocq (if not the earliest detective, one of the first) in 1818 France as he and that narrator, Hector Carpienter investigate the possibility that Hectors father helped Louis Charles (Louis XIV and Marie Antoinettes son) escape from prison after the French Revolution.  

 The story is fascinating, with interesting characters and vivid descriptions, as are all of Baynard's books. It's really a great mystery, especially if you like historical fiction.  This Baynard guy is going places, his books are a step above the historical mysteries I've seen around recently.