This is a tough question because of the intricate nature of Roy's work. She provides no easy answers. In my mind, I think that if there is one source of evil or a location for it, the class system and system of social stratification based on caste might be a good candidate for where evil lies. The system of segregation that was imposed on the Indians by the British was internalized to the point where such divisions ended up demarcating personal relationships. It is for this reason that Vellya Paapen kills his son, and why Ammu and Velutha are punished so harsh for what they do in the hopes of transcending it. The fact that individuals take this social segregation into the realm of the private and into their own states of being, internalizing the failures of society as personal shortcomings, becomes a main reason for the evil and cruelty in the novel.