As the logic of evolution comes to a head in the middle of the Nineteenth Century, an older Frenchman, haunted by an odd event in his youth, tracks the journey of a strange stone object westward to a pre-Civil-War America. There he and his cousin, a young scientist, and a strong-willed woman they meet under trying circumstances match wits with a wealthy European entrepreneur to try to prevent, if they can, the possible loss of one world and the uncertain birth of another.