La Tua Cantante (The Reckoning)

The Secret was supposed to stay in the family.
Bella Swan spent her senior year falling for a "Cold One" and nearly losing her life to a nomadic tracker. She thought she was the only one in the Swan family with a magnet for trouble. She was wrong.
Enter Juniper Lyra Swan, the younger Swan sister.
While Bella was busy worrying about her soul, Juniper Lyra Swan was busy cataloging local legends and tracking heat signatures in the woods of Forks. She doesn't just believe in the supernatural-she's obsessed with it. So, when a frantic trip to Italy leads her into the heart of a medieval fortress, she doesn't scream. She takes notes.

The Volturi have a rule: The secret must be kept.
Usually, humans who step into the throne room leave in pieces. But when Lucian, the Volturi's most lethal Leader, finds himself staring into the eyes of a girl who isn't afraid of his fangs-but instead wants to know the exact PSI of his bite-the ancient laws begin to blur.

A dangerous game of cat and mouse.
He is a predator who has forgotten what it feels like to be fascinated. She is a girl who refuses to be prey. As the Volturi realize that the youngest Swan knows more about their world than most vampires, Lucian must decide: is he protecting the law of his coven, or the human who has finally made his cold heart beat with frustration?

"Bella wants to be one of them. I just want to know how they work. And if the man in the black cloak thinks he can scare me off with a snarl, he clearly hasn't seen my research on ancient Italian burial rites."