The Queen's Key — Mary-Ellen Lang Collura

Caught between what she knows and what she is not supposed to know; torn between the dangers inside the Wall and the mysteries beyond it; trusted by Rogues and Rejects but not her own father, Zabeth searches for the truth in a world that has lost it. Life in an emerging social order is hard enough for a feisty, motherless girl. But then an alien civilization from across the Shallow Sea appears and all hell breaks loose.