by instinct and urges just as every other animal is.  The work of Sigmund Freud had essentially reduced human beings and human behavior to our sexual desires.  Works like these made it seem all the more necessary to police morality, and the potential difference between what one could observe versus what was going on behind closed doors made many uncomfortable. 

In other words, it was entirely plausible to think that a man who presented to all the world a scrupulous and upright persona could, underneath that facade, actually be devoid of morality.  Thus, when Mr. Enfield explains to Mr. Utterson why he refers to a particular home as the "Black Mail House," his way of accounting for the strange occurrences he's observed is characteristic of this era.  He describes once seeing a horrible little man emerge from that door and trample a little girl.  The man would have continued on, but passers-by stopped him and insisted that he offer some financial remuneration to the child's family.  This horrid man disappeared into the door of this house and emerged shortly thereafter with a check signed by a reputed local doctor.  Mr. Enfield says that the little man

"was a fellow that nobody could have to do with, a really damnable man; and the person that drew the cheque is the very pink of the proprieties, celebrated too, and (what makes it worse) one of [those] fellows who do what they call good.  Black mail, I suppose; an honest man paying through the nose for some of the capers of his youth."

Therefore, Mr. Enfield automatically attributes this strangeness to the belief that Dr. Jekyll must have some skeletons in his closet, some indiscretion(s) from his past that he would wish to hide, and this terrible man must know it and be using the information to blackmail him.  To leap to such a conclusion might seem strange to us, now, but it seems to make perfect sense to Enfield, and to his auditor, Mr. Utterson.

For later generations, the Victorian era has been associated with a rigid formality within society and a degree of repression about subjects such as sex, which began to be dealt with much more openly in literature and in the public consciousness after Queen Victoria's death. To an extent, our view of that period is correct. Underneath a strait-laced exterior, one can often sense in nineteenth-century literature a latent violence and immorality which authors were not permitted to deal with explicitly. This dichotomy between exterior calm and interior passion and forbidden thoughts is expressed in Stevenson's Doctor Jekyll and Mister Hyde.

Though the story (or the split between Jekyll and Hyde) is emblematic of a duality in the Victorian Zeitgeist, this does not mean that Stevenson necessarily had to set his novel in the London of his own time. The slightly earlier tales of Hawthorne, for instance, which are similarly themed, are often set in a vague past, though they involve speculative science, as does Stevenson's novel. The combination of futuristic science with Gothic horror is typical of the period. But the familiarity of the setting in the case of Jekyll and Hyde ironically makes the horror stronger; the present-day backdrop of modern rationality in what was then the largest city in the world makes the strangeness and terror of the situation stand out in relief, as it were. Later in the century Bram Stoker accomplished the same thing in Dracula, juxtaposing modernity with ancient superstition and horror. In Dracula, a vampire exists in a world where modern inventions such as the railway, the typewriter, and the medical ability to transfuse blood are integral parts of the narrative. So it is with Stevenson. The centerpiece of his novel is a series of scientific laboratory experiments, but the result is a catastrophe in which man's primitive instincts are unleashed, to his own destruction.

Victorian-era London is an appropriate setting for this novella because it was during the latter part of Queen Victoria's reign that highly moralistic language and behavior became the social norm and expectation.  Published in 1886, Stevenson's work falls squarely within this period.  The Victorians were quite concerned with proper dress and proper speech, but -- most importantly -- proper conduct.  Citizens were expected to repress anything improper, especially salacious desires.  Sexuality, especially, was taboo.  This is why Henry Jekyll feels such a strong desire to extract the part of himself that drives him to do improper things and destroy it.  

For many people in this era, strict moral rules didn't actually stop them from doing "bad things," it just meant that those things occurred behind locked doors and were not spoken of.  Jekyll, in trying to keep with established ethical mores of the day, only wants to actually be the morally upright doctor that he portrays to the world; however, it is too difficult to repress his urges and so he attempts to kill the part of himself that responds to those desires.  Were it not for his society and time, perhaps Jekyll would not have felt so keenly the necessity of abiding by the rules; if his society did not insist on the bottling-up of any desire not in keeping with the strict moral code, then he might not have resorted to such a dangerous course of action.  It is, likely, his setting which actually prompts him to feel the necessity of attempting his experiment.