A Choice of Gods

One night in July, 2135, there were some eight billion people on Earth! The next morning there were perhaps 400. There was no clue to what had happened to the world's population—but, over the centuries that followed, still stranger things occurred.

The human lifespan now stretched to millennia instead of decades, and much of the remaining population developed the ability to move at will among the stars—and abandoned their homeworld for a life in deep space.

Then, after 3000 years, a star-rover discovered what had happened to Earth's original inhabitants—and that they were coming to reclaim their heritage. Those who had stayed behind knew, with a growing fear, that the mystery of what had been done to Earth and why was about to be solved... in a way that would change humanity forever.

Synopsis from Open Library.