The prototype time/space transport device has been judged by the councils as too dangerous to risk using. Thalesian historian Pi-Sigma Avalon cannot resist the temptation. Just one quick jump, back to Old Earth, the lost world of their past, shrouded in mystery. No one need know. But he stays much longer that he intends, and comes back changed. With him is Dr. Eloise Smith, an Old Earth human who confounds their expectations of that primitive species...