Derek Prince details his beginning experiences with the casting out of Demons.  He was a new Pastor at a small church.  A woman in the congregation release a horrifying shriek during one of his sermons.  He was confronted with a choice.  Allow his fear from lack of experience dealing with these kinds of problems cause him to back down from this confrontation with evil.  Or he could summon his courage, trust Christ and attempt to expel the Demon possessing the woman.  This was his beginning of a search for and answer to the question "Are Demons real?"