Unhallowed ground / Heather Graham.

Enhanced descriptions from Syndetics:

New York Times bestselling author.When Sarah McKinley is finally able to buy and restore the historic Florida mansion that she has always loved, she dismisses the horror stories of past residents vanishing and a long-dead housekeeper who practiced black magic. Then, in the midst of renovations, she makes a grim discovery. Hidden within the walls of Sarah's dream house are the remains of dozens of bodies - some dating back over a century.The door to the past is blown wide open when Caleb Anderson, a private investigator, shows up at the mansion. He believes several current missing persons cases are linked to the house and its dark past. Working together to find the connection and stop a killer, Sarah and Caleb research the history of the haunted house as their attraction grows. But despite their best efforts, the truth eludes them. There is one who knows the truth - a spirit who follows their every move. Soon Caleb begins to fear that if he can't stay a step ahead, he could lose Sarah to a killer with an ability to transcend time in a quest for blood and sacrifice.