After the events in Riven, Atrus returns to D'ni in an attempt to rebuild the fallen civilization. With a small group of assistants, he and Catherine find stable Ages and search for survivors of the fall. Together, this larger group begins documenting stable Ages and rebuilding the fallen city.
While in construction, a room is discovered that contains a mysterious linking book. After extensive attempts to get into the room, the linking book is recovered. It leads to the Age of Terahnee, where Atrus and his followers are welcomed by the aristocratic natives. Enamored of the opulent lifestyle, Atrus asks, and receives permission to relocate his people onto Terahnee; but soon learns that all of Terahnee's architectural and technological feats are accomplished by slave-labor. Shortly afterward, the ruling class of Terahnee are rendered extinct by a bacterium (harmless to the D'ni, and to the slave-class as well), and Atrus is consulted by Gat, the leader among the newly-freed subordinate class, to help them build a new and better society. When the intermediate class of overseers ('P'aarli' in the Terahnee language) attempt to claim power, Atrus and Gat send the militant 'Ymur' at the head of an army, to destroy them; and when Ymur, after this victory, declares himself dictator, he is challenged by Atrus and Gat, but killed by his own subordinates. All the survivors thereafter relocate to other Ages, and seal the links with Terahnee. An epilogue, narrated by Catherine, argues that the D'ni Prophecies, which seem to foreshadow the pandemic on Terahnee, are badly-reconstructed copies of a literary corpus similar to that of the linking books; but intended rather to reach other times, than other Ages.