c) The end of the story is unhappy, and somewhat shocking. While the reader expects Peyton Farquhar to live out the rest of his life, he is hanged, his escape being only a hallucination.
b) The episodes are all relevant to the total meaning. Each section has its own purpose: part one describes what is occurring, part two gives the background behind the occurrence, and part three gives Peyton Farquhar's hallucination and the plot twist.
a) The plot has unity in the sense that all parts, and ideas within the parts, are relevant. It may seem to be not unified because it is not in chronological order.