After 20 years, a vanished space voyager returns to Earth bearing a dangerous truth that will alter the universe in this powerful, thought-provoking science fiction classic from one of the golden age greats.

Twenty years ago, Asher Sutton vanished somewhere in the star system 61 Cygni, an inaccessible corner of the universe that humankind has thus far been unable to explore. Now Asher has returned to Earth, having impossibly survived catastrophic damage to his spacecraft. But the star traveler is not the same man he was when he began his journey two decades earlier. He is, in fact, no longer completely human. And he isn't alone. But he has a message to convey that could have reality-altering consequences for the human galaxy conquerors who consider themselves almost gods and for the nearly human androids they create, enslave, and oppress.

It is Asher's destiny to change everything. His mission has made him a hero to some, a pariah to others - and a target for determined time-traveling assassins from the future whose mission it is to silence him at all costs before everything they cherish is obliterated.

A true science fiction visionary, SFWA Grand Master Clifford D. Simak infused thrilling stories of time travel, space exploration, artificial intelligence, and alien contact with powerful, thought-provoking ideas. An enthralling masterwork of speculative fiction that astonishes while exploring humanity in all its disparate aspects, Time and Again can be counted among the prolific, multiple Hugo and Nebula Award-winning author's most brilliantly imagined and successfully realized creations.