Books in the Nightingale Series series

ER Nurse Desiree O'Rourke and Dr. Gaston Bissett have spent the last few centuries laying low and saving lives-and taking them. Spending the past two years at University Hospital in Shreveport, LA has been peaceful, until Desiree starts to sense the workings of their nemesis, Kristoff, a 500-year-old alchemist that specializes in mind control. Kristoff has made it his mission to cause as much terror to the vampires' lives as possible and take out thousands of humans in the process. With the help of humans, Joe Pascal and Shauna Norris, Desiree and Gaston want to end Kristoff's terror for good, but will they succeed before Kristoff takes out the entire hospital?