With their father and brother taken from them, the royal Eddon twins Barrick and Briony have done their best to hold the kingdom together. But now Barrick has been captured in a failed war against the immortal Twilight People and Briony has been forced to flee the castle. Old magics are stirring beneath the ancient castle and behind the Shadowline, and the machinations of gods, fairies, and mortals threaten to spread devastation across the entire world.