The Adventuress by Tasha Alexander

Jeremy, the Duke of Bainbridge, Emily's dearest friend has finally gotten engaged. To an American heiress no less. But Emily's not sure she can like the girl. Not because she's an American, rather because the woman can't seem to hold an opinion of her own. Instead, Amity (the fiancee) transforms to agree with whoever is talking to her.
The book opens with the death of one of Jeremy's closest friends. The authorities presume suicide but Emily isn't so sure. And there seems to be some darkness lurking underneath the cheerful facade of this honeymoon party.
The story is told in alternating first person (Emily, in the "present") and third person (Amity, snippets of the months leading up to the party). It's an interesting way to sow some red herrings quite nicely into the story.
I think regular Alexander readers will be quite satisfied with this book.
This book comes out next Tuesday, October 13, 2015.