Taking its title from Yeats' poem The Second Coming the story mirrors two intertwined tales about the protagonist Ogongkwo amongst the Ibo of Nigeria in the 1890s. First as tale of the individual's role in and conflict with society and then about the individual and the clash of civilizations.
It's a surprisingly deep and nuanced tale, sadder for the reflections Achebe probably had from his own life under Colonialism in Nigeria.
It makes it on more than a few top 100 lists and quite frankly not enough good African authors get exposure, so give it a read if you get the chance (in that same vein, I'd also recommend Naguib Mahfouz as well.).