Robert Louis Stevenson 
The Strange Case of Dr. Jekyll and Mr. Hyde [EPUB ebook] 

The Strange Case of Dr Jekyll and Mr Hyde is a gothic novella by Scottish author Robert Louis Stevenson, first published in 1886.
It is about a London legal practitioner named Gabriel John Utterson who investigates strange occurrences between his old friend, Dr Henry Jekyll, and the evil Edward Hyde.
The novella’s impact is such that it has become a part of the language, with the phrase 'Jekyll and Hyde’ entering the vernacular to refer to people with an unpredictably dual nature: outwardly good, but sometimes shockingly evil.