Ferdinando Cefalù is desperate to marry his cousin, Angela, but he is married to Rosalia and divorce is illegal in Italy. To get around the law, he tries to trick his wife into having an affair so he can catch her and murder her, as he knows he would be given a light sentence for killing an adulterous woman. He persuades a painter to lure his wife into an affair, but Rosalia proves to be more faithful than he expected.
The film presents the tale of Agnese Ascalone, daughter of prominent miner Vincenzo Ascalone, and takes place in a small town in Sicily. Agnese is seduced by her sister Matilde's fiancé, and has a tryst with him for which she confesses and tries to repent, only to be discovered by her mother and father.
Several people disappear from and at the sea. Their bodies are found gnawed to the skeleton, even the marrow is missing. The scientists have no idea which animal could do such things. Dr. Turner begins to suspect that the company which builds a tunnel beneath the bay might have poisoned the environment and caused an octopus to mutate to giant dimensions...
