Finished on 7/14/09:

THE BLACK TOWER by Louis Bayard, 2008.
An excellent historical mystery concerning the son of Louis XVI and Marie Antoinette, who was incarcerated in the Black Tower, and after his parents' deaths, allegedly died there a short time later. This story, set in 1818, involves Vidocq, the chief of the Parisian plainclothes police force, who is on the trail to find out if this prince has somehow survived death. A murdered man has been found with a paper on him containing the name of Hector Carpentier, and that's where Vidocq's search begins. This Hector is the son of another Hector Carpentier, who was the prince's sympathetic physician in the tower. These two characters become involved in a dangerous and tangled quest to find out the truth of what actually happened to the prince: is he dead or alive? Where is he? Who is he? And who is behind the series of attacks and murders against those who are out to either discover or conceal the truth of the matter? Great details of Restoration France, intriguing historical premise, fast paced narrative, and colorful characters (Vidocq is definitely interesting), make this a good read.