The Demon You Know by Christine Warren

As a research grunt at a local television station, Abby Baker tends to blend into the background, which is where she’s most comfortable. But when she ends up being the last resort to cover a hot story, Abby discovers a whole new side to her personality when she is possessed by a fiend—a type of rogue demon. Suddenly everyone wants a piece of her. And now the demon Rule—also a hunter of his own kind who have gone astray—is Abby’s only hope…

The "Others"--that is, vampires, werewolves, fae, and all manner of supernatural beings have made the choice to reveal themselves to the human populations, and are still fighting for equal rights etc. Rule is a demon--but demons in this series are for the most part counted among the good guys. Rule in particular makes a living protecting his world and the human world from the dark, dangerous, and more or less evil fiends. Abby is an ordinary human who ends up possessed by a fiend, Lou. Lou is in hiding because he possesses knowledge of a spell that could give power into the hands of the most sinister of all fiends. Abby is quickly taken under the protection of rule and his friends--a band that includes many Others introduced in previous books.

 I enjoyed this addition to the series, but not as much as I have liked others.