P.C. George Dixon (Warner) is a long-serving traditional copper who is due to retire shortly. He takes a new recruit under his aegis and introduces him to the easy-going night beat. Dixon is a classic ordinary hero but also anachronistic, unprepared and unable to answer the violence of the 1950s.

When an undersea volcano sends tremors throughout the Atlantic, aquatic creatures come out of hiding. Merchant seamen Joe Ryan and partner Sam Slade harness the most unusual of the lot, a massive beast that looks like a Tyrannosaurus Rex. The enterprising sailors deliver their quarry to a British circus, but it turns out that the animal is a newborn. And, when his much larger mother arrives in London to rescue her son, the city feels her wrath.