TENTACLES

People are turning up dead at Solana Beach, a seaside tourist resort, their skeletons picked clean of flesh and bone marrow. The local sheriff Douglas Robards has no leads, but newspaper reporter Ned Turner suspects the construction of an underwater tunnel by the Trojan company, owned by Mr. Whitehead. Whitehead threatens Turner to leave it alone, but after several more deaths, he interrogates killer whale trainer and marine expert Will Gleason.

When two of Gleason's divers are also killed, Gleason goes to investigate for himself and determines the attacks are the result of Trojan using ultrasonic drilling techniques with which the sound waves have been "above regulated levels", which maddens a giant octopus, causing it to attack and devour human swimmers and boaters whenever it feels similar frequencies. Criticizing him for risking his life, his wife Vicky joins her sister Judy at the pool. When Judy goes on a boating expedition and also goes missing, Vicky goes in search and is also killed by the octopus.

In the meantime, Turner's sister Tillie has taken her young son Tommy to a boating race, which is attacked by the octopus and from which Tommy is one of the few to miraculously survive. Gleason vows to kill the octopus and takes his trained killer whales out to where Vicky was killed. In the end, the octopus is killed by a pair of killer whales while Gleason tries to save Mike, another diver.

The giant octopus is killed by a pair of trained killer whales, who attack it while Will Gleason tries to save another diver.

The climax turns the tables on the monstrous threat by leveraging marine intelligence—killer whales—against the mutated octopus, reinforcing the theme of nature both as a victim and an avenger of human interference. The resolution underlines the consequences of environmental negligence, with the human characters relying on animal allies to restore balance after corporate carelessness nearly devastates the community.