Scientist Steve Karnes delivers a speech to a British scientific society, led by Professor James Bickford, about the dangers to marine life posed by nuclear testing.

Before Karnes can return to the United States, a real-life example of his concern materialises when a fisherman in Looe, Cornwall is killed on the beach, and his dying word is "behemoth".

Karnes and Bickford try to persuade authorities to close the River Thames, but the military officer believes that their radar tracking systems will be enough to detect the behemoth and prevent it from getting near the city.

As Karnes and Bickford climb into a car to leave the area, they hear a radio report of dead fish washing up on the eastern shores of the United States.

In an odd connection between O'Brien and his most famous creation, stock screams that were used in King Kong can be heard in the scenes where the creature attacks the ferry and when it invades London.

[4] In the book Video Movie Guide 2002, mention of the stop-action animation was made, but with the proviso that "the film monster wasn't bad but Willis O'Brien was clearly working with a low budget".

[7] The Monthly Film Bulletin wrote: "This is considerably better than many recent essays in monster science-fiction, both in its suspense and staging; but the story, though put over as convincingly as possible, remains stuck at routine outsize-palaeontology level.

No offense to the Brits, but watching a bunch of folks stand around and keep the stiff upper lip while radioactive monsters from the deep attack London isn't too much fun".