In the quiet seaside town of Weymouth a pack of unruly Teddy Boys, led by the surly King (Oliver Reed), use the sexy 20-year-old Joan (Shirley Anne Field), the sister of the incestuous King, to lure a seemingly wealthy middle-aged womanizing tourist named Simon Wells (Macdonald Carey) away from the promenade where they mug and beat him. The beaten Simon is brought by military security officers to be assisted by his sculptress friend Freya (Viveca Lindfors) and a scientist named Bernard (Alexander Knox), who are drinking at a local hotel. For some inexplicable reason, Joan tries to tempt the dirty old man, Simon, again when she sees him by his yacht. When her snarling thuggish brother spots her, he threatens her if she doesn’t leave the yacht. But Joan tells the dropout from the world of insurance executives to take off for the sea, she wants to be free of her brother’s maniacal guardianship. With the gang looking for them, the two would-be lovers hide in Freya’s studio located near the side of a cliff. When the gang discovers their whereabouts, they run from her brother and all three fall from the cliff into the sea. They are rescued by nine strange eleven-year-old children, who live in a hidden cave and have body temperatures that are ice cold. Soon they uncover that the children are mutants, as their parents died when exposed to radiation and that Bernard and a military team are conducting secret experiments with them to see if they could possibly create “a new kind of man” to survive a nuclear attack. Whoever comes into contact with the children and is not wearing radiation gear, will die.