1960s' sci-fi drama following American tourist Simon Wells (Macdonald Carey) and 20-year-old Joan (Shirley Anne Field) as they escape a motorcycle gang. Joan is the sister of gang leader King (Oliver Reed) and she falls for Simon when King and his cronies mug him. The two become an item and set sail in Simon's boat in an attempt to evade King's wrath. Their journey leads them to a military base where scientist Bernard (Alexander Knox) is performing experiments on children in the hope that he can create a generation that will survive a nuclear bomb. When King catches up with the couple, they persuade him to help the children escape but the task is seemingly impossible. While on the base Simon, Joan and King are all exposed to radioactivity. Will they be able to avoid capture and survive its effects?