Andre Norton 
The Defiant Agents 

Travis Fox, Apache Indian and an expert in time travel, volunteers for a mission to colonize the planet of Topaz. But when he and his fellow Apaches find themselves reverting to the ways of their ancient warrior race, Fox suspects that a dangerous force is responsible–and that there’s more at stake than just their lives.

Circa l’autore

Andre Alice Norton (born Alice Mary Norton, February 17, 1912 – March 17, 2005) was an American writer of science fiction and fantasy, who also wrote works of historical fiction and contemporary fiction. She wrote primarily under the pen name Andre Norton, but also under Andrew North and Allen Weston. She was the first woman to be Gandalf Grand Master of Fantasy, first to be Sfwa Grand Master, and first inducted by the Science Fiction and Fantasy Hall of Fame.