Enchantress from the Stars, by Sylvia Louise Engdahl, 1970

A dragon threatens Goeryn’s village, and none who venture to slay it return; Medical Officer Jarel regrets joining the colonizing expedition to Andrecia, where Imperial fire-breathing machinery devours the virgin landscape; Federation Field Agent-to-be Elana stows away on a mission to save the planet Andrecia from colonization. Heroes from different worlds and phases of societal evolution come together on pristine Andrecia in an ambitious braiding of narrative styles, viewpoints, and philosophies. A modern retelling of “The Fairy Queen” enabled by futuristic science fantasy, and an argument for ethics, and enlightened faith, to restrain and direct mankind’s march toward progress.