What is the main conflict in The Comedians by Graham Greene?

The Medea, a Dutch ship traveling from the US to Port-au-Prince carries Mr.. Brown, Mr.. and Mr.s. Smith, and Major Jones among its passengers. They entertain themselves in various ways, mostly discussing their experiences. Mr.. Smith is a presidential candidate in the US 1948 elections. He wants to establish a vegetarian center in Port-au-Prince. Mr.. Brown returns from the US, where he unsuccessfully tried to sell his hotel in Haiti losing money due to the violent regime sparking fear in everyone, including tourists. Major Jones is on a secret business mission.