Lilith, daughter of a siren, sacrificed her voice at thirteen to save her three pirate foster brothers from the sea monster Kraken, becoming mute. After five years of waiting, she is betrayed and humiliated by the brothers—now obsessed with the ship's prostitute Lucy—on her coming-of-age day. Broken-hearted, she tosses her bridal garland to Kai, the Crown Prince of Atlantis disguised as a poor sailor, and seals a blood contract with him. When she cries "I regret it," her vow breaks and her siren voice returns. Kai marries her with all his devotion, abolishes the death contract, and rewrites maritime law. During Kraken's rampage, Lilith sounds the sacred horn and sings the Siren Song to calm the deep—then ascends the throne of the sea with Kai, while her three remorseful brothers are condemned to keep the lighthouse lamp for life.