Louis Bayard’s The Black Tower (2008) is set in 1818. A young medical doctor, Hector Carpentier, is recruited by Vidocq—considered the originator of criminology, the founder of the French national police force, and the first private detective—to investigate if Louis XVII is still alive.

Officially, Louis XVII died as a 10 year old boy in 1795 but there has long been speculation he was smuggled out of his prison cell and raised in informal foster care.