Book in a Series - Revenants

Don't you hate it when you are reading a book and it's part of a book series and you have to wait FOREVER for the next book to come out.  Then you get the next book and you can't remember where it left off?  Well I'm going to summarize a book in a series that I've read so that when I get the next book I can look at my summary and know what happened.  Warning, the following contains spoilers!

Revenants
Die For Me - Amy Plum
 
Until I die - 2012

Kate's parents die in a car crash and her & her sister a sent to Paris to live with their grandparents.  While in Paris she meets a mysterious boy named Vincent.  She quickly finds out that he is a revenant (a being that sacrifices himself to save people that are dying, in the process they die and come back to life.  Each time they die they come back the age that they originally died.  There are also bad revenants that kill people.  The good ones are always battling the bad ones. 

Here sister gets caught up with the bad ones and Kate saves her and she finds out the truth.