It is the year 1891 and a military doctor, Lieutenant Claude de Ross (Claudio Cassinelli) a survivor of not one, but two shipwrecks, washes ashore on a mysterious, uncharted Caribbean island along with a handful of convicts. When several of these convicts meet unfortunate ends at the hands of the titular fishmen, Claude and the other survivors flee into the jungle, only to encounter the sadistic Edmond Rackham (Richard Johnson) and his beautiful captive Amanda Marvin (Barbara Bach). 　　Amanda's father, Professor Ernest Marvin (Joseph Cotten), a once-famed biologist, has discovered a way to transform humans into amphibious creatures and controls their every move. Rackham manipulates Marvin into performing the procedure upon both willing and unwilling participants by assuring him that his work is undertaken for purely scientific and humanitarian motives (Marvin hopes to reduce strain on the world food supply by creating a race of people who can live in the resource-untapped ocean). Having discovered the lost city of Atlantis beneath the waters surrounding the island however, Rackham is in actuality using the half-human monsters to plunder the lost city of its treasures. 　　Shakira (Beryl Cunningham), a voodoo priestess in the employ of Rackham foretells death and destruction descending upon the island. 　　The priestess' prophecy is fulfilled as the film ends with Claude and Amanda attempting an escape from a gun-wielding Rackham, a crazed Shakira, uncontrolled fishmen and the very volcano that doomed Atlantis which awakens and threatens to send what unsubmerged landmass remains to oblivion. 　　译文(3): 1891年，一位军医克劳德·德·罗斯中尉（克劳迪奥·卡西内利饰）和几名罪犯一起被冲上了一个神秘的、未知的加勒比海岛屿，他不是一次，而是两次沉船事故的幸存者。当这些罪犯中的几人在有名无实的渔夫手中遭遇不幸时，克劳德和其他幸存者逃到丛林中，却遇到了虐待狂的埃德蒙德·拉卡姆（理查德·约翰逊饰）和他美丽的俘虏阿曼达·马文（芭芭拉·巴赫饰）。