Daughter of Crows - Mark Lawrence

The plot jumps between different timelines to reveal how Rue became a "Kindness," a terrifying agent of vengeance. In the past, she was one of a hundred girls sold to an academy where only three are allowed to survive and graduate after ten years of bloody training. In the present, the story follows Rue’s mission for retribution as she deals with the physical limitations of her ageing body. It is a powerful tale about memory, the weight of a violent past, and the burning rage that can drive a person even in their final years.