E.C. Tubb 
Terridae [EPUB ebook] 
The Dumarest Saga Book 25

Zabul was no ordinary world. It was a private religious sanctuary — location secret, visitors unwelcome. It was a world fanatically dedicated to one belief and to one goal. The belief that mankind originated on a single world . . . the goal was to find it.To find Earth was a goal that Earl Dumarest shared. But how much did he really have in common with the zealot Terridae, who slept in caskets decorated with the zodiacs and dreamed of soaring towers of crystal and floating cities? And what were their despotic Guardians really after?(First published 1981)