一个心灰意冷的救援潜水员再次出手，救友于鲨口，而他要面对的是被认为早已灭绝的庞大巨齿鲨。

Researchers on the undersea lab Aquatica have genetically altered the brains of captive sharks to develop a cure for Alzheimer's disease. But there's an unexpected side effect: the sharks got smarter, faster, and more dangerous. After a big storm damages their remote research facility, they must fight for their lives.

On a volcanic island near the Kingdom of Hetvia rules Count Dakkar, a benevolent leader and scientist who has eliminated class distinction among the island's inhabitants. Dakkar, his sister Sonia and her fiance, engineer Nicolai Roget have designed a submarine which Roget pilots on its initial voyage just before the island is overrun by Baron Falon, despotic ruler of Hetvia. Falon sets out after Roget in a second submarine and the two craft, diving to the ocean's floor, discover a strange land populated by dragons, giant squid and an eerie undiscovered humanoid race.