On the surface this – one of Simak’s better novels – is a complex and intricate tale of time-travel and paradox. Simak is very much a pastoral writer, in that his SF is often set against a backdrop of solid American rural values, and though he never preaches, his writing nevertheless extols the virtues of tolerance and pacifism.
Six thousand years in the future Earth is at the centre of an interstellar Empire, clinging to control of the galaxy with the help of androids who are only differentiated from true humans by their inability to reproduce and the tattoos on their foreheads. Asher Sutton, a reconnaissance agent, has been missing for the last twenty years after being sent to 61 Cygni to assess an alien planet which may or may not pose a threat to the stability of Human Culture.
Sutton’s boss, Adams, receives a visit from a mysterious stranger claiming to be from the future, who predicts Sutton’s imminent return and tells Adams that Sutton must be killed to prevent him from writing a book which will plunge the Human worlds into war.
Sutton’s not-yet-written book is a Bible which explains our relationship with these creatures, a philosophy which could destabilise Human control of the galaxy, since it espouses equality of all life, including androids.
The book itself, copies of which Sutton discovers before he has even begun to write it, is the reason why various factions, including the androids and groups from other periods in time are eager to either kill Sutton or use him and his ‘revised’ book for their own devices.
Like most Simak novels, it’s an affirmation of the basic goodness of human nature and a very ‘cosy’ novel.