What is the main conflict in Nightmares & Dreamscapes by Stephen King?

Robinson is a third grade school teacher who becomes obsessed with avenging his wife's premature death. Elizabeth, Robinson's wife, was a witness to a criminal act committed by a high level gangster named Dolan. Elizabeth, wanting to do the right thing, reports the crime to the police and FBI and agrees to testify. Elizabeth car blows up and she dies.