The Fury and the Power. The Fury, #3

Eden Waring has known fear in her life. She is an Avatar, a talented young psychic with the ability to produce at will her doppelganger - her mirror image, who calls herself "Gwen" and possesses remarkable powers beyond even Eden's gifts. Gwen can be invisible to mortal eyes, if she chooses to be, and can even travel back and forth in time. As gifted as Eden and Gwen are, there is an even stronger entity that stalks them, coveting Gwen's unique talents.
He is known as Mordant, the Dark Side of God, a being both ageless and deadly, so evil that his soul was split in two by the Caretakers, ancient souls in surprising positions of earthly influence, who are charged to watch over humankind. In order to regain his full potential for destruction and reach his goal of world domination, he must accomplish two goals: seduce Eden Waring through any means necessary and take away Eden's control of her own doppelganger.
In human form, Mordant is the ultimate trickster: handsome, wealthy, charming. But when he is provoked, he is nothing but deadly. Eden is his unwitting prey, stalked from the barren Rift Valley of Kenya to the holy streets of Rome, and finally to the neon glitz of Las Vegas, where a terrible and frightening reckoning is waiting to pounce on them both.