After French Prince Louis betrays and murders pirate queen Anna, her siren sister Lydia disguises herself as Anna to infiltrate the royal court. Enduring Louis's cruel abuse and uncovering his dark secrets, Lydia seeks to reclaim her stolen siren heart. As Louis attempts to execute her and seize power, Lydia awakens her terrifying deep-sea magic, unleashing a devastating storm to expose his crimes and exact a brutal, magical revenge.