Sara Zarr tackles big issues in her books, and this one is no exception. Sam is a pastor's daughter whose mother is in rehab. She feels pressure to be the perfect daughter and feels like an outsider among her friends who see her "differently." Then a local teen goes missing, and Sam understandably begins to question her faith. Her father seems to be able to counsel everyone else, but can't talk to his daughter.
I think every person, sometimes during their teens, begins to question the faith to which their parents have exposed them. This is a normal process, even without the turmoil that Sam experiences in Once Was Lost. The book does a good job dealing with these issues and adds additional drama to keep the book exciting. It is definitely a "girl book" and students who like reading about teen issues will enjoy this one.