This is one of the best Soviet science fiction books. Imagine you are sent to undeveloped planet where people still live during what looks like Earth's middle ages as a mere observer (think Prime Directive from Star Trek). You are so good at being undercover that you make real friends as well as real enemies. What happens if your enemies start killing your friends and drag the society back to dark ages in the process? You have god-like powers to stop bad guys, would you use them?
The book combines fast-paced action with deep philosophical questions successfully, something very few books manage to pull off. Highly recommended.