Floats the Dark Shadow - The Paris Trilogy, #1

Young American painter Theodora Faraday struggles to become an artist in Belle Époque Paris. She's tasted the champagne of success, illustrating poems for the Revenants, a group of poets led by her adored cousin, Averill. When children she knows vanish mysteriously, Theo confronts Inspecteur Michel Devaux who suspects the Revenants are involved. Theo refuses to believe the killer could be a friend—could be the man she loves. Classic detection and occult revelation lead Michel and Theo through the dark underbelly of Paris, from catacombs to asylums, to the obscene ritual of a Black Mass. Following the maze of clues they discover the murderer believes he is the reincarnation of the most evil serial killer in the history of France—Gilles de Rais. Once Joan of Arc's lieutenant, after her death he plunged into an orgy of evil. The Church burned him at the stake for heresy, sorcery, and the depraved murder of hundreds of peasant children. Whether deranged mind or demonic passion incite him, the killer must be found before he strikes again.