What is the theme in The Ox-Bow Incident by Walter Van Tilburg Clark?

Vigilante Justice is a central theme in this story. Many Western movies show men hanged at the drop of the hat for reason varying from stealing, cheating at poker, to murder. In this novel, the author explores the impact of such an act. A well liked cowhand is rumored to have been shot in the head by a cattle rustler who has been targeting local ranchers all winter. This man's closest friend, Jeff Farnley, vows to get revenge. Farnley has little hope that the legal system will bring these men to justice. Soon others join him in the immediate excitement over the situation. In a matter of minutes a mob forms.