Hard to be a god by Boris Strugatski

Don Rumata has been sent from Earth to other planet, to the medieval kingdom of Arkanar with instructions to observe and to save what he can. Masquerading as an arrogant nobleman, a dueler, and a brawler, he is never defeated, but yet he can never kill. With his doubt and compassion, and his deep love for a local girl named Kira, Rumata wants to save the kingdom from the machinations of Don Reba, the first minister to the king. But given his orders, what role can he play? This long overdue translation will reintroduce one of the most profound Soviet-era novels to an eager audience.

The premise of this story seems like a grand adventure. Scientists and observers from a future paradise earth infiltrate and study other earth-like planets. Their main principle resembles Star Trek's 'prime directive' of non-interference.

But this is not another peaceful little kingdom they study. The world itself is breaking down. Warlords, such as the vicious Don Reba, hunt down and destroy any person who can read or write. That world is a lump of filth, a place in rapid and horrific decline. Language itself is breaking down, collapsing into grunts and single phrases. And for the scientists who are observing this, for our fake Don Murata, it is hard to be a god, to stand by and watch as people destroy themselves. He can try and save a few literates and talk to them, but they slip through his grasp and fade into oblivion...