In the Blood (Jefferson Tayte Genealogical Mystery) by Steve Robinson

Jefferson Tayte is a genealogist who is hired by a wealthy family to find out if they are related to a family England who are very powerful.  Jefferson goes to England and finds out there is more to the family history than he bargained for.  He meets up with a woman named Amy and finds out that her husband died by finding something in the house that could destroy the family in England.  It opens up up a dark secret that the England family has been hiding for years.