At the height of his power, King Louis XIV (Pierce Brosnan) believes that the only way to protect the future of France is by securing his reign for all of eternity. After receiving careful council from his best men, he decides that the only way to protect the future of his crown is to take the life force of a beautiful mermaid (Fan Bingbing). The French Navy, led by their most capable seaman, Yves (Ben Walker), is sent on an epic quest to capture a mermaid and bring her to Versailles.

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Meanwhile, Marie-Josephe (Kaya Scodelario), a young, free-spirited beauty, and illegitimate daughter of King Louis is taken from the strict confines of a cliff-side convent and sent to the King’s court to settle the King’s war debts through an arranged marriage. Fate intervenes when Marie-Josephe discovers the mystical mermaid. Marie-Josephe does not know she is the daughter of the King, what he has planned for her, or why the King has imprisoned such a majestic creature. As her bond with the mermaid grows, Marie-Josephe falls in love with Yves, the seaman commissioned to keep the mermaid captive, and at the risk of her own life and his freedom, she must defy the King to set her soul mate free.