Shadow Queen

The eccentric old lady who contacted Wild-Freeman Publisher's bestselling author might have been crazy, but she was, beyond a doubt, dead. Her ramshackle house contained her corpse, her fey daughter Marie, and a locked box purported to hold the famous "Casket Letters," the damning evidence that condemned Mary Queen of Scots to death. Lost for four hundred years, they could make a blockbuster of a book and put Wild-Freeman in the black at last. Diana Speed, the company's chief financial officer, knew it was a publishing coup to kill for--but not that murder was part of the package. Now terror was stalking the strange, ethereal Marie, whose looks and behavior eerily mimicked the long-dead Queen...the author, whose secret deals were turning sour...and Diana herself, who could give up the letter's or fight for her life in a plot that led to the royal family itself.

This is #1 in Diana Speed Series.