Nightingale

Being Sidhe is hard, but a Sidhe without a heartbeat?

Life is lucrative and easy for Dr. Grace Caldwell--daughter of vampire father and fey mother--until her ex-boyfriend, FBI agent Jack Montgomery, blackmails her into helping him solve a prostitute's murder. If only she wasn't as attracted to Jack as ever, she could concentrate on finding the murderer and get back to her regularly scheduled life. And then there's the vampire Constantine, seductive and powerful, a family friend she's supposed to marry...

Not much of a vampire, and clueless about her fey powers--if she has any--Grace must journey to the Sidhe and enlist the help of the fey to unravel the riddle of the murder. She and Jack might just get killed, but then, two worlds depend on her success. If she fails, both her worlds and all of humanity will descend into chaos of epic proportions.