Robert Louis Stevenson's dark novellaA long short story or short novel. tells of a scientist's haunting search for the truth of human nature. People, says Dr Jekyll, are "commingled out of good and evil". But his attempts to separate the two sides cause him to be consumed by a devilish, murderous alter egoAn alternative self. called Mr Hyde. The idea that pure darkness could lurk beneath the most civilised personality was particularly chilling for Victorian readers.
Jekyll and Hyde

Glossary
Novella - A long short story or short novel.
Alter ego - An alternative self.
Manifestation - An event or object that clearly shows an idea.