When numerous people go missing in a seaside resort town, reporter Ned Turner (John Huston) helps to uncover the reason -- a gigantic rampaging octopus. As the eight-legged monster continues to terrorize the coast, marine biologist Will Gleason (Bo Hopkins) attempts to devise a way to stop the octopus before more tourists fall victim to the creature. Meanwhile, it appears that a corporation headed by Mr. Whitehead (Henry Fonda) may be connected to the cephalopod's violent behavior.