Seduced By Shadows
This book was above me. There's really no other way to put it.
In a war amongst demons, those wishing to atone and those who just want to be the evil that they are, Archer feels a new possession is about to happen. When he finds Sera to be that target, the first woman target in ages, he knows it's a sign that things are changing. And so he goes to her, and warns her that darkness is coming. Once it's done, he'll return for her.
If the demon that possesses her is a djinn, he must destroy her. If teshuva, then she will be recruited into their army, to forever fight the eternal good v evil fight, in all of its shades of gray glory.
This book is a long one, which was felt. But also goes to hint than anything could happen. Which did. Death and betrayal. Which I was *so* not ready for, neither of them.