Generations of clones on the moon chronicle the recovery of mother Earth, which has been destroyed and deserted. Eons have passed and a new generation of clones discover that their own base on the moon had been destroyed in the past and then rediscovered and rebuilt by the man known as Sandor Pen.
 
In the meantime the remnants of humanity have just started unlocking the mysteries of interstellar flight, but over the years their memory of old Earth has faded ... a memory Sandor Pen intends to reignite.

The Ultimate Earth is classic Williamson. A multi-layered story with subtle interpretations. The novella was published to much critical acclaim, winning both the Hugo and Nebula Awards.