This book has many problems. Oh so many problems.
The premise is that Morgan Kingsley is an exorcist. Demons exist and can be invited to possess someone, but if they break the rules (for example, killing a human) they can be exorcised. They can also be exorcised for possessing an unwilling host. If a demon touches a human's bare skin, he can possess her.
The story opens with Morgan performing an exorcism in a town that rarely has to deal with them, so they are not well trained. In the course of the exorcism Morgan is touched, but the demon starts to back off on his own, something that would only happen if Morgan were already possessed. Since possession by a demon means the host's personality and will is if not exactly destroyed than at least heavily suppressed, she would know if she were possessed.
She calls in her friend, another prominent exorcist to prove that she's not possessed. Her friend, Val, performs a ceremony saying she's clean so Morgan can go home to her boyfriend.
The demon enforcer, Adam, whose job it is to keep demons in line, asks Morgan to perform an exorcism. His demon lover, Saul, who was in Dominic's body (it was a willing possession) had killed a number of humans in self defense because a religious anti-demon hate group had beaten him nearly to death and he snapped. But it doesn't matter if the deaths were in self-defense or not. He still killed a human. So Morgan exercises him and for the first time feels some sympathy for demons.
When performing an exorcism, there's a high chance that the exorcism will leave the host in a coma or severely brain damaged. Fortunately, Dominic survives intact.
Of course, it turns out that Morgan is possessed, by the King of Demons, no less. She was drugged and possessed against her will, but her will was so strong that the demon, the King of Demons, mind, can't suppress her personality and take over her body. The demon, Lugh, can't communicate with her directly so he starts leaving her notes and she has to find out if she's crazy or really does have a demon. Once the demon is verified she has to figure out why he was forced into her in the first place and how to get him out.
Black's mythology makes no sense. The demons say they aren't inherently evil, and they're certainly not the demons that appear in Christian mythology. Okay, fine. The appearance of demons on the scene of human affairs appears to be an extremely recent development, but there's absolutely no explanation for why demons revealed themselves.
When a demon possesses a human, the human is granted supernatural strength and healing so often people in dangerous jobs such as firefighters, policemen, etc, are inhabited by demons. It's clear to me (sort of) what humans get out of it, but it's a lot less clear why demons would care enough to inhabit a human.
Lugh mentions at one point that there's no physical sensation in their dimension so young demons often go off the deep end when they first inhabit a body. So is that supposed to be the only reason they want human bodies? There's really no other explanation offered for what demons find so attractive about inhabiting humans and apparently there are so many of them that want to do it that there aren't enough willing hosts.
One of the things that Morgan finds so abhorrent about demon possession is that they suppresses the personality of the host. But clearly that's not the case with Lugh and Morgan, and Dominic says some things that make it pretty clear that it wasn't true for he and Saul either. Similarly, Adam makes a few references to his hosts feelings. So clearly, the host is still there and able to communicate on some level. Dominic must have had some control over his own body because he mentions a couple of times when Saul shielded him (physically or emotionally) from things.
Morgan's brother, Andrew, invited a demon, Raphael into his body and from what I can tell in the book, Andrew's personality was totally suppressed. So it's not a matter of whether or not the demon was invited in willingly, and surely it can't be a matter of the strength of the demon since Lugh is one of the most powerful demons out there and yet can't takeover Morgan's body, at least until he's been in it for quite a while and even then his control isn't perfect.
It's also not really explained what exorcism is. Is it spiritual, magical, just a matter of will? Can anyone train to do it? If it's magical, it's the only non demon magic in the book.
Moving on.
I really don't get what Morgan is supposed to see in her boyfriend. Our first in person introduction to him (after some phone sex) has him showing up at the airport when she's expressly asked him not to because she wants to be alone for a while. Then he embarrasses her at the airport because, he says, sometimes that snaps her out of a mood. But we never see that him embarrassing her does anything other than piss her off so he really just ends up looking like a giant ass who only cares about his own pleasure.
There's a lot of graphic sex in the book, and a little goes a long way. Especially when she's staying with Dominic and Adam and finds out that they're into S&M. She's strongly repulsed by it in the "ew that's icky!" kind of way. Granted, Adam is a bastard about it, playing while she's in the next room and can't leave. But still. There's a lot of "S&M is creepy and icky!" If it was a single scene where she said hey, not my thing and moved on it would have been fine. And then when Adam and Dominic do play and have sex in the room next store, she's really turned on and masturbates to it. Apparently it's never occurred to her that she might find two guys together hot. Maybe I've just read too much slash, but really? She'd never considered it before?
And there's a scene where she lets Adam whip her (I don't remember why. In order to get him to do something). So she doesn't actually want it, he knows she doesn't want it, but since she's agreed to it he's fine with doing it. I don't think consent under duress is really consent. He apparently doesn't whip people who don't give consent and maybe he doesn't care if consent isn't the same thing as willingness or desire but in my book, consent under duress when both people know that's the only reason consent is given, is no consent at all so proceeding is rape.
I'm also not sure why he wants to do it in the first place. With Dominic there's a sexual element, but there's no sexual element with Morgan.
And at one point they go to an S&M club which is just more "ew, icky" and Adam is forced to have sex with Dominic in public in yet another scene that has murky consent and seems awfully close to rape. Especially since he never prepares Dominic before fucking him, not that the author mentions what a problem that would be even if Dominic were truly willing.
And at the end of the book she decides to leave the boyfriend so he'll be safe which I always think is a dick move. One person shouldn't get to make a unilateral decision like that, certainly if she leaves with absolutely no explanation.
It's really too bad. The overall plot sounds kind of interesting and I like the idea of the law needing to evolve but the world is clearly not well thought out or well built and the gratuitous sex scenes are a real turn off.