At the heart of the story (somewhere you can find that this is a novel) lies the theme of duality. In the Victorian literature, we can find many examples of duplicity: from Stevenson to Dickens, from Bram Stoker to Henry James, from Joseph Sheridan Le Fanu to many other authors. The Victorians believed that human nature is dual, and they could not speak directly about sex and sexuality.
Stevenson in the " The Strange Case of Dr. Jekyll and Mr. Hyde” depicts a bifurcated human nature literally: Dr. Jekyll, with the help of a special mixture, liberates his vicious part, or rather, he physically reincarnates and becomes Mr. Hyde.
Dr. Henry Jekyll has a wonderful opportunity, on the one hand, to remain the same virtuous Jekyll, on the other hand, to satisfy his inner being, thirsting for perverted pleasures. It all sounds to be perfect, but once Hyde commits a murder.
He was a large, well-built, youthful man of about fifty, with a face that may not be quite open, but, undoubtedly, clever and kind.
The goal of Stevenson the artist was in "the fantastic drama that unfolded in the presence of ordinary sensible people", in the familiar atmosphere of Dickens's readers, where he amidst a cold London fog, ugly houses, serious elderly gentlemen sipping an aged port, family lawyers and devoted butlers, on background of hidden vices lurking behind the walls of rich mansions, where Jekyll lives, cold dawns and dapper skins.
To gradually create a world in which a strange transformation from the words of Dr. Jekyll would be perceived by the reader as a good artistic reality, to make the reader be informed of such a mood, when he doesn’t ask whether such a transformation is possible, Stevenson applies a variety of techniques - images , intonation, figures of speech and, of course, false moves, that mainly appears on the character of Dr. Henry Jekyll.
Henry Jekyll in the Essays