Franklin (Samuel L. Jackson), the owner of a biochemical pharmaceutical factory, provides a large amount of funds for Dr. Susan McAlester (Saffron Burrows) to study drugs against Alzheimer's disease. Susan and her research team extract proteins from shark brains and inject necrotic human brain cells in a well-equipped underwater research center. In order to extract more shark brain protein, Susan also increases the brain capacity of the sharks. This move makes the sharks, which were originally used as test subjects, stronger and smarter. Shark expert Carter (Thomas Jane) discovered the abnormality of the sharks when he was with them day and night, and warned Susan, but Susan ignored it. Finally, in the last experiment, those ferocious sharks who had become human test subjects retaliated against humans...