The Darkness Within Us by Tricia Levenselle

The Darkness Within Us is a wickedly delightful companion novel to Tricia Levenseller's The Shadows Between Us.

Chrysantha Stathos has won.
By hiding her intelligence and ambition behind the mask of a beautiful air-headed girl, she has become a wealthy duchess. And, once her elderly husband dies, she will have all the freedom, money, and safety she’s ever wanted.

Or so she thought.
A man claiming to be the estranged grandson of Chrysantha’s lecherous late husband has turned up to steal her inheritance. To make matters worse, her little sister is going to be queen and is rubbing it in her face.

Chrysantha decides that the only thing to do is upstage Alessandra at her own wedding. And as for this grandson, he has to go. Never mind that he’s extremely handsome and secretive with mysterious powers . . . No, Chrysantha wants Eryx Demos dead, and in the end, a Stathos girl always gets what she wants.