Sisters of Salt and Iron - Kady Cross

Lark Noble is finally happy. She's trying to move on and put the events of the past behind her: the people who avoided her because she talked to the ghost of her dead twin sister, the parents who couldn't be around her anymore and even the attempt she made on her own life. She finally has friendspeople who know her secrets and still care about herand she has Ben, the cute guy she never saw coming.

Wren Noble is lonely. Unable to interact with the living, she wants to be happy for her sister's newfound happiness, but she feels like she's losing her. It doesn't help that Kevin, the very not-dead guy she was starting to fall for, seems to be moving on.

Then Wren meets Noah, the spirit of a young man who died a century ago. Noah is cute, he's charming and he makes Wren feel something she's never felt before. But Noah has a dark influence on Wren, and Lark's distrust of him drives the sisters apart for the first time in their lives. As Halloween approaches and the veil between the worlds thins, bringing the dead closer to the world of the living, Lark must find a way to stop whatever deadly act Noah is planning, even if it means going through her sister to do so."