What is the main conflict in People of Darkness by Tony Hillerman?

The People of Darkness are a group of people in a peyote church who survived an explosion at an oil well because a peyote induced vision warned them not to go to work that day. These men would later die of cancer, a highly unusual event that would lead tribal police officer Jim Chee to realize that something more sinister than nature is at work here. People of Darkness is a tightly plotted novel that takes the reader from mere curiosity into the heart of a culture where motives as simple as greed are rare and seen as the sinister acts of a witch.