by Robert Silverberg
Media: Mass market paperback
Cover art: (unknown)
They had fought a life-crushing 21st century dictatorship. Now they were political prisoners, exiled to an Earth before the dawn of life. Sentenced to the past, sealed forever behind a billion-year-high wall of time, they had to make their home by the grey slab shorelines of a barren planet. A lifeless world was their prison, eons away from cities and civilizations and trips to the stars—and there was no way back.
Then one day the stranger came...