Humanity has triumphed over all obstacles. The world has been united in peace. Information is transmitted from person to person in an instant, and they now rule the earth without an exclusive government. Only two things remain to hold back humanity's progress-death and intergalactic travel. But can the group that changes these last remaining obstacles survive an accident that removes them from their world? What will happen to the world's time line when six immortals find themselves in pre-history? Will the lives of their youth hang in the balance of their ex post facto actions?