On the Hawaiian island of Niihau, biologist Max Varian and Navy diver Liz Tayler are in charge of a United States and Japanese joint attack dolphin research program. When a Japanese fishing vessel is sunk off the coast of Maui, the program leader, Okada Takahashi, sends his team to investigate. More deaths begin to occur in Maui waters, leaving the only surviving witness, Mya Kendig, traumatized and searching for answers.

Okada's team soon discovers a cryptozoological creature is responsible for the attacks. A creature legend calls the most powerful underwater being. A creature possessing the power to make modern technology useless. With limited options and both governments wanting the creature's existence kept secret, the team begins training the dolphins on a new task: to hunt and kill the master of all water creatures.