While on holiday in Weymouth, American boat owner Simon Wells (Macdonald Carey) is mugged by bike gang leader, King (Oliver Reed), found by two army security officers from a secret project near the town and, on being taken to a hotel to clean up, meets Bernard (Alexander Knox), the scientist in charge of the project, and his girlfriend Freya (Viveca Lindfors), a beautiful sculptress who occupies a cottage built into the cliff nearby.
The next day, King’s sister, Joan (Shirley Anne Field) comes to see Simon, and when her brother’s gang follow her she goes out to sea on his boat.
They land along the coast and go to the cottage to hide from the gang. After dark they leave and are chased once more by the gang.
Going over the barbed wire surrounding the secret project’s headquarters, they and King fall over the cliff into the water.
All three are rescued by a group of children – eerily cold-blooded, who take them to their quarters, carved out of solid stone in the cliffs.
Bernard, knowing the children are radioactive (the secret project is a government programme in which radioactive children are being schooled to repopulate the planet after a nuclear war) makes desperate efforts to get the adults out, but they misinterpret his motives and escape with the children through an entrance to the caves behind Freya’s cottage.
Bernard and his men arrive and recapture all but one of the children, who escapes with King in Freya’s car. Men in helicopters rescue the child and then force King to plunge the car off a bridge.
Simon and Joan are told that they will die of radiation sickness and can go off in their boat. Bernard then asks Freya to forget what she has seen, but the woman refuses and he is forced to shoot her in order to keep his work secret.
The plot – which mixes romance, doom-laden science-fiction, elements of a British Hells Angels exploitation movie and a state conspiracy potboiler – never really fuses.
Shirley Anne Field