Seeking a book about post-apocalyptic humans abducted by aliens, with a "mockbuster" title

Question

I am trying to remember a novel that I read some of. I think I got it from my uncle's collection, which would mean it was published before 1975, and I was reading it before 1990. I don't remember that much of the plot, except that it involved a primitive tribe of humans (who seemed to be living on a post-apocalyptic Earth), who were visited by what were clearly identifiable (to the reader) as humanoid aliens, who arrive and begin kidnapping people. A human warrior stows away in the aliens' travel device to try to figure out what is going on and to rescue the kidnapped people.

That was pretty early in the book, I think, but it's where I stopped reading. I stopped because I had only been reading the book because I thought somebody had recommended it to me; however, that person had actually meant a different SF book with a similar name. In fact, I think the name of the book I am thinking of was probably deliberately confusing, like "mockbuster" movies.

Answer 1

Possibly The Slaves of Heaven by Edmund Cooper

Post apocalyptic story where people living aboard a huge space station kidnap people from the primitive tribes living on the Earth for breeding purposes.

"They were the Night Comers. No one could say if they were ghosts or gods or devils. They only knew they came from the sky, silver clad, ominous, with a Medusa glance that could freeze a man in his tracks. They stole women and carried them off to heaven, decimating the Earth's population and threatening the survival of the human species.

Berry, chief of the Londos clan, frustrated by the uselessness of his tribes' primitive weapons, ventures into the inner circle of the Night Comers and is spirited away in their ship to their home in the stars. There, Berry's fight for survival holds the key to the existence of his own world and that of the Night Comers as well.."

The 'Night Comers' are humanoid robots carrying out the commands of their masters in the orbital station.