What is the conflict in City of Joy?

City of Joy, by French author Dominique LaPierre, was published in 1985. It is considered a novel, although LaPierre relates true stories of his experiences in Calcutta and uses the names of real people.
The novel unfolds through the stories of three characters—a priest from Poland, an Indian rickshaw puller, and an American doctor—all living in Calcutta for their own reasons. The overall conflict that the novel explores is the stratification of society along socioeconomic lines and among religious beliefs. Even among the poor in the slum Anand Nagar, LaPierre observes that there are levels of poverty, from the working poor to the abject, and that instead of solidarity there, caste distinctions further separate people who are all struggling. In this way, the book transcends the common trope of the rich exploiting the poor and authorities doing little to prevent the injustice (though this is part of what LaPierre documents).