Casey is eighteen years old in a post-nuclear world - where twenty is old age. Casey's real name is K/C-4(SCI). He's a supergenius, created in a test tube from the best genetic material available. He lives in an underground complex under what was once Colorado, along with other survivors of World War III. The colony's population is slowly dwindling. Casey himself is eighteen, and aging fast. According to the best calculations, he will die in exactly eight months and fourteen days. But why? Casey thinks the answer lies somewhere in the past, and he builds a time machine to take him there. The risks of time travel are enormous, yet Casey can't help himself. He becomes involved in the fate of a twentieth-century family, and with one girl in particular. It soon becomes clear that the future of Casey's colony depends entirely on the decisions he makes.