After landing on Cambria, Zoe realizes she can’t spend the rest of her life as the source of a rivalry between the two men she loves, so she volunteers for Peyton’s army, which threatens her relationship with Adrian. But after five months of fighting the darkness that has repeatedly tried to drown her, she needs her own justification for escaping an invasion few humans survived. 
Protecting those who are left gives Zoe a new sense of purpose, but she is quickly confronted with the realities of what took place on Cambria when this planet was invaded, and she will soon discover if she is capable of being the savior of her people she desperately wants to become.