Please help me find this story!
I'm basically going to say what I remember from it. First of all, it was a M Shadows story and from what I remember it even had a part two. It wasn't really romance and it touched some pretty dark themes. Shadows and the gang were some sort of demons and the main female character was a police officer.
The main character's father (back when she was young) had some deal with Shadows and one time she went downstairs she met him (again, as a child). Her father was killed and she ended up going to college to become a police officer of some sort. As her first assignment she has to infiltrate a prison that was actually a town ruled by Avenged Sevenfold.
Now, these are some scenes I remember, but they may not be very accurate.
In order to enter the city-like prison, she acquired a key for the gate. After deciding to park her car at a safe distance and leaving her stuff inside, she managed to get in.
Another scene is when she entered a popular club (Radiant Eclipse maybe? There were a lot of names based off of the band's song names) known to be frequented by the town leaders. All inmates had a code stamped on their neck (like a barcode I guess?) and as she didn't have one, she lied to the bouncer and said she was new and had covered it with makeup.
She gets to meet some of the guys and gets kidnapped by them and taken to Shadows. I believe he rapes her on her first night as his captive after being injected with some serum so she doesn't become pregnant for a few days.
This is mostly what I remember from the story. I also think that at some point she turns into some type of demon too and that she also had some sort of friend/help that was a male, but I'm not too sure.
It was quite a long story and it was either rathed R or NC-17 because of scenes related to blood, violence or rape.