The Start of Eternity/The End of Eternity

At the end of Isaac Asimov's time travel story, "The End of Eternity", he wrote about the spread of humans off of Earth and to other worlds of the galaxy as constituting "the beginning of Infinity". Asimov wrote a great saga of human colonization of the galaxy and humanity's spread to 25,000,000 Earth-like planets: the Foundation Series. In the 20,000 year history of the Galactic Empire, as depicted by Asimov, there was no mention of intelligent, human-like beings from other worlds. Then, in the last pages of the Foundation Series, Asimov raised the specter of alien beings from beyond our own galaxy.

The Start of Eternity continues the Foundation saga by telling the story of those alien beings and their interactions with humanity.