The Thesis of Silas Black. Annals of S.O.L.M., #4

Possession is a long con. As Maggie Stone struggles to understand her new world, she quickly realizes that demons aren't the only creatures manipulating mankind. Vampires not only exist but also have an entire social order, and one of the most powerful vampires on earth has done something uncharacteristic: she's let a newborn feed on her, accidentally giving this young woman unspeakable power but no control.
Since Maggie's body is synthetic, John Pinkerton decides to use her to lure this newborn away from the various factions that would use both her naivety and her strength to accomplish their own ends. At the same time, Silas Black, a serial killer turned hitman, not only finds himself inside a synthetic body but also has an entire horde of demons enticing him toward some greater plan. The main entity, who calls itself Rachel, continues to tell him that the synthetic bodies, transfer devices, and plans he's stolen are not worth his time.
She has a larger plan for him-a plan and a great game. Rachel wants him to seduce a newborn vampire. And new bodies aren't the only thing Silas and Maggie have in common. They share a link that allows them to communicate. The two souls trapped in synthetic bodies must find a way to outwit the other as they navigate their new world, each trying to win the young woman who has the power to destroy it.