Joyce Maynard, in an interview about After Her: "I am not a writer of crime fiction. And I am not ultimately interested in the mind and actions of a psychopath as I am in the mind and actions of so-called ordinary people." 
 Thus the resulting novel : a portrait of two sisters and their bond, of the imagination and preoccupations of young girls, of naivete, innocence, and the inevitable loss of both. This is a coming-of-age story in a thriller setting (I kept picturing a copy of Judy Blume's Are You There God? It's Me, Margaret and a dvd of the psychological thriller Zodiac stuck in Joyce Maynard's blender and whirled around for 300 pages). She does the coming-of-age bit quite well, the thriller bit, less so, which makes for a novel that straddles the genres and is ultimately "good!" but not great.