Kate Daniels is a mercenary - a monster killer for hire - in a world in flux. Alternating waves of magic and techology began to wash over our world a few decades back and the magic is gradually winning out. In its wake a lot of the old nightmares from mythology have awoken.
As if her day job wasn't dangerous enough, Kate is hiding a secret that could get her killed - and the more she gets dragged into events the more likely that secret is to come out.
The world of Kate Daniels is brilliant. It reminds me a lot of Shadowrun except without the cyberpunk. The vampires are particularly interesting as mindless inhuman creatures driven by bloodlust and piloted necromancer 'navigators'. But there is a vast host of other monsters as well, drawn from mythology familar and obscure.
Kate is the very model of a misanthropic kick-ass urban fantasy heroine - except that unlike many of them, she is likable, complex, and well-written. And while she often does outrageous and downright stupid things, she is motivated in ways that we can understand and which feel realistic for her character. Plus, her dry sense of humor really shines through.
The chemistry between Kate and her main squeeze Curran is strong - in fact, downright hostile a lot of the time - but their relationship grows slowly over the series while the focus remains on the action.