Martino is a young child who claims to have an invisible friend called Luca. His parents assume it is just a game, but strange things start to happen.

In Rome, a vagrant finds the body of a teen girl, her throat professional slashed. Police inspector Olmi uses his brutal and violent methods to follow a trail that leads him toward high government officials. When his methods leave an innocent bystander dead, the corrupt officials have an excuse to get Olmi transferred to a coastal town where the pace is slow and he has time for a romantic dalliance. Soon, Olmi discovers that fishing isn't the only local occupation, and out comes his gun and his ruthless tactics of investigation.

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...