The Touch of Twilight (Sign of the Zodiac, Book 3)

On the surface she's a sexy, sophisticated socialite, at home among the beautiful people of the Las Vegas upper crust. But Joanna Archer inhabits another world: a place ordinary humans cannot see . . . a dangerous dimension where an eternal battle rages between the agents of Light and Shadow. And Joanna is both.
Stalked by an enigmatic doppelganger from a preternatural realm, Joanna can feel the Light failing—which is propelling her toward a terrifying confrontation with the ultimate master of evil, the dark lord of Shadow: her father.
Vegas is all about winning big . . . or losing everything. To save her friends, her future, her worlds, Joanna Archer must gamble it all by fully embracing the darkness inside her.