What is the main conflict in the novel, The Cold Dish?

The Cold Dish is a mystery in which Sheriff Walter Longmire must investigate two possible revenge murders. Two of four boys guilty of raping a young girl are murdered. The sheriff must figure out which one of the many suspects wanted them dead. The motive is obviously revenge since the boys had gotten off lightly for the crime they committed. Longmire needs to put his own feelings aside and bring the killer to justice.