Coastal cities around the world are flooded overnight, and Dr. Mara Voss (Angelina Jolie) uncovers a shocking new species of mermaids—creatures designed by nature to restore the balance humans have disrupted. Led by the terrifying Nerida (Megan Fox), the mermaids possess bioluminescent armies that sing ships into the abyss.

Dr. Elise Hart (Scarlett Johansson), a rebellious xenobiologist, believes there may be a way to communicate with them—until she discovers that Nerida can imitate human voices and faces, stolen from drowned victims.

With the oceans rising and entire nations falling under attack, the last hope rests with Mara, Elise, and their dwindling team, as they venture into a submerged megacity to destroy the mermaid queen’s control.

In a heart-stopping final battle within a spiraling coral throne room, the survivors must choose: save the world from the mermaids, or let the oceans reclaim their throne.