Something very big and very dangerous is swimming in the seas of planet Aqua Minor. It's destroying all of the fish factories and making mincemeat out of all the submarines. So Captain Teggs and the brave crew on the DSS Sauropod set off to investigate.

What do they find? A gigantic liopleurodon has made Aqua Minor its home. At first all the evidence points to him as the culprit behind the mass destruction. But then new evidence is uncovered that shows it couldn't be the liopleurodon. Is another monster lurking beneath the seas as well?