The Question and Answer section for The Outcasts of Poker Flat is a great resource to ask questions, find answers, and discuss the novel.
The citizens of Poker Flat are reacting to and acting against the people in town that they consider undesirables. A secret committee was put in charge of cleaning up the town and removing people of questionable character.
I believe that was Tom Simson, a young man who lost his fortune.
The characters are actually forced to leave. After a string of robberies in town, prominent people used Mr. Oakhurst, the Duchess, Mother Shipton, and Uncle Billy as scapegoats to rid the town of "improper persons".