In Search of the Rose Notes, by Emily Arsenault

When a brilliant author takes on the mystery genre, the results can be staggering.  In Search of is set in three time frames:  before the disappearance of Rose, the babysitter of two paranormal-obsessed young teens, Nora and Charlotte; after Rose's disappearance, when the girls try to use the paranormal to solve the mystery; and in modern day after the discovery of Rose's body, when Nora returns to her hometown of Waverly to tread over old ground with Charlotte.  The impact of Rose's disappearance on Nora and Charlotte and their friends is cataclysmic, and it seems to take all of Nora's hard-won self-possession to face Waverly again as an adult.