The House Saphir - By Marissa Meyer

Mallory Fontaine is a fraud. Though she comes from a long line of witches, the only magic she possesses is the ability to see ghosts, which is rarely as useful as one would think. She and her sister have maintained the family business, eking out a paltry living by selling bogus spells to gullible buyers and conducting tours of the infamous mansion where the first of the Saphir murders took place.
Mallory is a self-proclaimed expert on Count Bastien Saphir—otherwise known as Monsieur Le Bleu—who brutally killed three of his wives more than a century ago. But she never expected to meet Bastien's great-great grandson and heir to the Saphir estate. Armand is handsome, wealthy, and convinced that the Fontaine Sisters are as talented as they claim. The perfect mark. When he offers Mallory a large sum of money to rid his ancestral home of Le Bleu's ghost, she can’t resist. A paid vacation at Armand’s country manor? It’s practically a dream come true, never mind the ghosts of murdered wives and the monsters that are as common as household pests.
But when murder again comes to the House Saphir, Mallory finds herself at the center of the investigation—and she is almost certain the killer is mortal. If she has any hope of cashing in on the payment she was promised, she’ll have to solve the murder and banish the ghost, all while upholding the illusion of witchcraft.
But that all sounds relatively easy compared to her biggest challenge: learning to trust her heart. Especially when the person her heart wants the most might be a murderer himself.