The Far Side of Evil — Sylvia Engdahl

THE FATE OF TORIS RESTS IN ELANA'S HANDS....
Elana, newly graduated from the Federation Anthropological Service Academy, is sent immediately into danger on the planet Toris -- a Youngling world poised on the brink of nuclear war. She is ordered to merely observe, and must not reveal her alien origin or interfere with the planet's natural course of evolution. But how can she stand by and watch as an entire world drives itself to nuclear annihilation?

Fellow agent Randil should never have been sent on this mission. He is not properly trained to work in the field, and his compassion for the Torisians may lead him to intervene. Yet his very actions may bring about the holocaust that he is so desperately trying to prevent.

Elana must make a crucial decision: side with a renegade agent, or stop him at any cost....