Karen Marie Moning Fever series

MacKayla Lane’s life is good. She has great friends, a decent job, and a car that breaks down only every other week or so. In other words, she’s your perfectly ordinary twenty-first-century woman.
Or so she thinks... until something extraordinary happens.
When her sister is murdered, leaving a single clue to her death–a cryptic message on Mac’s cell phone–Mac journeys to Ireland in search of answers. The quest to find her sister’s killer draws her into a shadowy realm where nothing is as it seems, where good and evil wear the same treacherously seductive mask. She is soon faced with an even greater challenge: staying alive long enough to learn how to handle a power she had no idea she possessed–a gift that allows her to see beyond the world of man, into the dangerous realm of the Fae...