What is the theme in A Simple Plan: A Novel by Scott B. Smith?

Greed is an important theme. While there's no doubt that some people want money - even a great deal of money - there is a difference between a simple desire for money and the level of greed exemplified by those involved in this story. The desire for money that provides a particular lifestyle is common to most people but outright greed is exemplified by actions that show no respect for others. It's interesting that both are seen in this story.