Dark Requiem (The Darkling Trilogy, Book 3‪)‬

Did she go too far?
Dallas Marshall is beautiful, rich and...relentless. Once she decides she wants to be with Avery nothing will stand in her way. But becoming a powerful vampire who cannot control her hunger threatens to push Avery further out of her reach. And that is not all. Dallas now finds herself up against an ancient evil that seeks to be reborn through her.
Can he let go of his lost beloved?
Avery's heart has grieved for Luna, his lost love, for decades. When Dallas forces her way into his life, he cannot deny the eerie similarities between the two unimaginably powerful and dangerous women. There are times when a quick smile, a turn of the head, makes him wonder: is Dallas merely a descendant of his beloved Luna...or is something far more insidious at work? It takes everything Avery has to control Dallas. Can he save her from the evil that has lived in darkness for centuries waiting for its chance to devour?
Its time has almost come.
Together or apart, Dallas and Avery will come face-to-face with old enemies and strange allies as they run headlong to the brink of death and beyond to battle the darkness which has slaughtered Luna's descendants for generations. And even then, the victory they have fought for may be forever denied to them. For nothing is as it seems.