Tobias's Sister- Divergent Story

Cassie is the sister of the dauntless prodigy Four. Her dad is Marcus Eaton. Her mother died when she was young. So she does not remember her. That is when Marcus started to beat them. It got worse every time. He blames them for there mother's death. Also he blames Cassie for her brother leaving to dauntless. Her brother leaves for dauntless. Cassie follows him two years later. What will happen when the war comes?