The guardian of Isis
In 2136 A.D. the settlers on the planet Isis, under the dominance of an absolute ruler, have lost all the technical knowledge of their forefathers and reverted to a primitive society dominated by myths and taboos.
Science fiction, Juvenile fiction, Isis (egyptian deity)
Monica Hughes        
Monica Hughes OC (November 3, 1925 – March 7, 2003) was an English-Canadian author of books for children and young adults, especially science fiction. She also wrote adventure and historical novels set in Canada, and the text for some children's picture books. She may be known best for the Isis trilogy of young-adult science fiction novels (1980–1982).

**Source**: [Monica Hughes](https://en.wikipedia.org/wiki/Monica_Hughes) on Wikipedia.