As is the case in many novels, minor characters such as these play an important role in establishing the milieu of the novel. This novel focuses on a young black homicide detective from Pasadena (Virgil Tibbs) who is passing through a fictional south Carolina town where a murder has occurred. He agrees to assist the inexperienced local police chief (Bill Gillespie). Themes of racial prejudice and suspicion of outsiders run through the book.
"Ralph works in a diner in Wells owned by Watkins, a city council member. [He] displays strong racist views in the opening chapter as well as when Sam purchases food from the diner clearly for Tibbs.
Harvey Oberst [was] the first official suspect in the murder investigation of Mantoli. Oberst was considered a primary suspect because he had Mantoli's wallet in his posession.
Delores Purdy [is] a young girl of eighteen, pretending to be sixteen because of her limited intellectual ability. Likes to parade in front of an open window during the early hours of the morning to attract potential viewers. Daughter of Mr. Purdy, a mentally challenged citizen of Wells.
Mr. Endicott [is] one of the more affluent citizens in Wells and [a] member of the city council. Lives in the outskirts of town. Provides a place for Duena to stay during the music festival. Endicott is the principal figure in bringing Manoli to Wells for the music festival.
Kaufmann, friend of the Endicott's and assitant to Mantoli, has a romantic interest in Duena."
https://en.wikipedia.org/wiki/In_the_Heat_of_the_Night_(novel)
