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.

P.C. George Dixon (Warner) a long-serving traditional “copper” who is due to retire shortly, takes a new recruit, Andy Mitchell (Hanley), under his aegis, introducing him to the easy-going night beat. Dixon is a classic Ealing ‘ordinary’ hero, but also anachronistic, unprepared and unable to answer the violence of Tom Riley (Bogarde). Called to the scene of a robbery at a local cinema, Dixon finds himself face-to-face with Riley, a desperate youth armed with a revolver. Dixon initially tries to talk Riley into surrendering the weapon, but Riley panics and fires. Dixon walks to his own death almost uncomprehending. Dixon is taken to hospital, but dies some hours later. The ending is another Ealing quirk, with ordinary decent society, including ‘professional’ criminals used to violence, banding together to track down and catch the murderer, who is trapped in the crowd at White City greyhound track in west London. To Andy Mitchell falls the honour of arresting Riley.