In many aspects of the novel, duality features as a device, used to intensify the effect of the plot. The theme runs all the way through the novel and can be identified on several levels. Stevenson, by integrating the theme of duality deep within his novel's plot, implies that all human beings have numerous and conflicting sides to their character.
The most evident type of duality in the novel is that of Dr. Henry Jekyll and Mr Edward Hyde, where the former is a respectable gentleman of the Victorian society and the other, a sinister character who lurks in the dark streets of the city. Dr Jekyll transforms into Mr Hyde, to behave in a manner which is more appealing to him yet in which he cannot behave without his disguise, due to the repressive nature of Victorian Society. Therefore, he, in he "thick cloak- of Mr Hyde, lurks in the sinister areas of London, such as Soho, without putting his reputation at risk. For all the characters in the novel, preserving one's reputation emerges as important. The prevalence of this Victorian value system is evident in the way that upright men, as Utterson and Enfield avoid gossip at all costs. They see gossip as a great demolisher of reputation. Similarly, when Utterson suspects Jekyll first of being blackmailed and then of sheltering Hyde from the police, he does not make his suspicious known. Part of being Jekyll's good and old friend, is a willingness to keep his secrets and not destroy his uprightness. The importance of reputation in the novel also reflects the significance of appearances, facades and surfaces, which often hide a sordid underside. In many instances in the novel, we can see that Utterson, true to his Victorian society, wishes not only to preserve Jekyll's reputation but also to preserve the appearance of order and decorum. .
Since the beginning of the novel, Dr Jekyll is aware of his dual nature, so he takes experiments to create a potion that will separate his good and evil side one from another.