The Slytherin Royals is in my opinion one of the best fan-fics out there. It blends the new OC into the story flawlessly and the plot line is amazing. the story is very smooth and gives a whole new perspective on the slytherin side of hogwarts and points out some issues with the school and justice system in the magical world of wizards and witches.
It is biased on slytherin but, I think you won't mind as it handles it pretty well and still shows that their still sometimes in the wrong. It also has some mention of murder and some bloody text but it handles it well.
the author of this amazing book is MaxineLane and all credit goes to her.
If you are a harry potter fan this book is for you.