To recount the plot seems pointless, but our dedication to our readers prevails. A seaside community called Solana Beach is plagued by mysterious deaths near the water. Judging from the film's title, it's the octopus, but the creature is driven to madness by vibrations from the machinery Trojan is using to dig an underwater tunnel. None of the film's characters figure out what is happening in a timely manner. Instead, we have to sit through an interminable number of scuba diving scenes.
Few things are as boring as filmed scuba diving.
People who are scuba diving have to move slowly, and they can't talk to each other. All they can do is look at things and occasionally point at suspicious holes in the sea floor. We found ourselves rooting for the horrible man-eating creatures that were no doubt lurking at the bottom of those holes. We kept waiting for those man-eating creatures to leap out at the stupid scuba divers, but Tentacles doesn't have the budget to show the giant octopus that is nominally the focus of the film. Most of the octopus' scenes are created by filming a normal octopus at the bottom of a aquarium, then editing these shots into the action featuring Italian actors.