John Glasby & A.J. Merak 
Dark Millenium [EPUB ebook] 

Planet Earth was finished, its surface seared by nuclear heat, its great cities obliterated, its billions of inhabitants dying or dead. Only a few pockets of survivors remained. For all but a few it was only a matter of time. Then into the poisoned atmosphere of Earth there flashed a mysterious craft from somewhere deep in space. It landed, a small number of Earth people were taken aboard, then the craft disappeared into the great void. During the dark millennium which followed a strange experiment was conducted. When it was complete, another space craft took off for Earth…