A Chinese-led international scientific research project was being carried out deep in the Mariana Trench when it encountered an unknown biological attack and researchers were trapped on the seabed. Jonas Taylor, a former U.S. Marine Corps deep-sea diving expert, was ordered to rescue him and once again encountered the prehistoric creature giant tooth shark that had left him an indelible memory in the deep sea a few years ago. Jonas teamed up with Zhang Suyin, a Chinese female scientist in the scientific research project, to successfully rescue the trapped people, but the rescue operation accidentally caused the megalodon shark to escape from the deep sea. When prehistoric giants return to the shallow sea, humans will pay a heavy price for their greed for nature...