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

Hank Mitchell, his older brother Jacob and Jacob's friend Lou are riding together in Jacob's truck when a fox runs across the road in front of them. The truck ends up in a snow bank and Jacob's dog runs after the fox. The three men go after the dog and after hiking about a half hour, find an airplane that has crashed in the woods. Goaded into going inside to check on the pilot, Hank finds the pilot dead and a duffle bag filled with money.