You Slay Me (Aisling Grey, Guardian, Book 1)

Aisling Grey is a courier enjoying a free, work-related trip to Paris when she learns she's a Guardian. That's a keeper of the Gates of Hell, for those who don't know. She finds this out from Drake Vireo, who's scrumptiously sexy-at least in his human form. Now Drake has stolen the package Aisling was sent to deliver, and she must track him down, get the package, and try to resist the passion boiling inside her.