The film opens with a mother playing with her baby near the ocean. A friend comes by so the mother literally runs 50 yards away to talk to her. One quick edit later and the baby is gone! Oh, the horror!!! Soon after, some dude disappears and the cops start wondering what the is going on?! Maybe it has something to do with that high frequency horseshit they're using in the underwater construction job going on nearby.
Made in California with Italian backing and an Italian crew/supporting cast, this movie looks cheap as fuck. All of the scenes with Henry Fonda are close-ups with him just talking on a phone or standing in a backyard. The Huston scenes aren't much better. There's never any good shots of the octopus. And what was up with the random freeze frames?! It was annoying as hell and made zero sense.
Not painfully bad, but I can't think of any reason for you to watch it...outside of the roaring octopus scene and Shelley Winters' ramblings. That's another thing that pissed me off: Shelley Winters didn't have any scenes with the creature. That would have been movie gold! Shelley Winters rolling around in the water wrapped up in the tentacles of a roaring giant octopus.
Zero nudity, zero quality special effects, zero suspense. Skip it or just watch it with friends to laugh at.
[Update: I just read an interview with Bo Hopkins in Shock Cinema that the filmmakers actually made a million dollar mechanical octopus...but it sank into the ocean. Also, the reason all of Henry Fonda's scenes have him sitting around doing nothing is because he'd just had a pacemaker installed.]
