The angel part of the book wasn't the whole main focus of the book. The main focus was a mystery and a search for a kidnapper/murderer.
Mercy is a fallen angel. She was cast out of heaven (for what, we don't know) and she doesn't really know exactly what she looks like. She has straight brown hair and brown eyes. Her real self, that is. Mercy "wakes" in different bodies all the time, ready to face a couple more weeks of a new life before moving on. She knows she has special powers, and she knows that she wants to find her beloved, Luc, who she only sees in dreams (don't worry, she's not totally focused on this aspect, especially after she meets Ryan...)
Mercy's current soul-jacking victim is a soprano named Carmen, who is off on a field trip to Paradise. Her host family are the Daley's who Mercy at once senses that they have very deep sorrows (she can sense stuff like that), and it doesn't take long to figure out - their daughter, Lauren, disappeared one night and is now presumed dead.
Ryan though, the only son of the Daleys, has never given up hope that Lauren is alive, somewhere. Mercy agrees to help him search for her.
All through the story, you've got this murder/kidnapping mystery at the front, but you've always got Mercy's search for herself somewhere in the background. We presume that she's a fallen angel of some sort, but we don't exactly know for sure. The book never totally spelled it out.
It's interesting to watch Mercy's transformation throughout the book. Living in too many lives and not having the chance to settle down has made her somewhat uncaring and detached. So it's nice to watch her transform into a slightly warmer person.
As for Luc, ugh. No. Why Mercy is interested in him I don't understand. I didn't like him. I reckon that later in the series he is going to turn out to be an evil, possessive demon-angel. I'm much more interested in what is going to happen with Ryan. Is Mercy going to try and find him? I hope so, because eternity with Luc would be so annoying. So, is this series going to let older characters make reappearances, or is it just going to be, like, new life, new situation?
I'm really interested to find out what happens in the next book. I would recommend this to 12+ year olds who want a mystery/paranormal kind of thing.