After the sinking of the submarine Siren 1, another submarine called Siren 2 is sent to search for it. The designer of the first submarine, Vic Hayes, is persuaded to join the expedition. The crew dives into an underwater crevice with great difficulty, scratching the hull slightly, and soon encounters the fact that at great depths there is life, and life is not friendly at all. After a series of dives, carnivorous seaweed is discovered, and a little later - a mass of malignant and flesh-hungry organisms, which are the result of genetic experiments on animals on the "Siren-1"....