Strange Case of Dr Jekyll and Mr Hyde is the original title of a novella written by the Scottish author Robert Louis Stevenson that was first published in 1886. The work is commonly known today as The Strange Case of Dr Jekyll and Mr Hyde, Dr Jekyll and Mr Hyde, or simply Jekyll & Hyde. It is about a London lawyer named Gabriel John Utterson who investigates strange occurrences between his old friend, Dr Henry Jekyll, and the evil Edward Hyde. The work is commonly associated with the rare mental condition often spuriously called "split personality", referred to in psychiatry as dissociative identity disorder, where within the same body there exists more than one distinct personality. In this case, there are two personalities within Dr Jekyll, one apparently good and the other evil; completely opposite levels of morality. The novella's impact is such that it has become a part of the language, with the very phrase "Jekyll and Hyde" coming to mean a person who is vastly different in moral character from one situation to the next.
In London, Gabriel John Utterson, a prosecutor, is on his weekly walk with his relative Richard Enfield, who proceeds to tell him of an encounter he had seen some months ago while coming home late at night from Cavendish Place. The tale describes a sinister figure named Mr Hyde who tramples a young girl, disappears into a door on the street, and re-emerges to pay off her relatives with 10 pounds in gold and a cheque signed by respectable gentleman Dr Henry Jekyll (a client and friend of Utterson's) for 90 pounds. Jekyll having recently and suddenly changed his will to make Hyde beneficiary, Utterson is disturbed and concerned about this development, and makes an effort to seek out Hyde. This is instilled by Utterson's fear that Hyde is blackmailing Dr Henry Jekyll for his money. Upon finally managing to encounter Hyde, Utterson is amazed by how ugly the man seems, as if deformed; though Utterson cannot say exactly how or why, Hyde provokes an instinctive feeling of revulsion in him. Much to Utterson's surprise, Hyde willingly offers Utterson his address. After one of Jekyll's dinner parties, Utterson stays behind to discuss the matter of Hyde with Jekyll. Utterson notices Jekyll turning pale, yet he assures Utterson that everything involving Hyde is in order and to be left alone. A year passes uneventfully. One night, a servant girl witnesses Hyde beat a man to death with a heavy cane. The man is MP Sir Danvers Carew, who was also a client of Utterson. The police contact Utterson, who suspects Hyde of the murder. He leads the officers to Hyde's apartment, feeling a sense of foreboding amid the eerie weather (the morning is dark and wreathed in fog). When they arrive at the apartment, the murderer has vanished, but they find half of the cane (described as being made of a strong wood but broken due to the beating) left behind a door. It is revealed to have been given to Jekyll by Utterson. Shortly thereafter, Utterson again visits Jekyll, who now claims to have ended all relations with Hyde. Jekyll shows Utterson a note, allegedly written to Jekyll by Hyde, apologizing for the trouble he has caused him and saying goodbye. That night, however, Utterson's clerk points out that Hyde’s handwriting bear a remarkable similarity to Jekyll's own. For a few months, Jekyll reverts to his former friendly and sociable manner, as if a weight has been lifted from his shoulders. Later, Jekyll suddenly begins to refuse visitors, and Dr Hastie Lanyon, a mutual acquaintance of Jekyll and Utterson, dies suddenly of shock after receiving information relating to Jekyll. Before his death, Lanyon gives Utterson a letter, with instructions that he not open it until after Jekyll's death and disappearance. Utterson goes out walking with Enfield, and they see Jekyll at a window of his laboratory; the three men begin to converse, but a look of horror suddenly comes over Jekyll's face, and he slams the window and disappears. Soon afterward, Jekyll's butler, Mr Poole, visits Utterson in a state of desperation and explains that Jekyll has secluded himself in his laboratory for several weeks. Utterson and Poole travel to Jekyll's house through empty, windswept, sinister streets; once there, they find the servants huddled together in fear. They go to see the laboratory where they hear that the voice coming from inside is not the voice of Jekyll and the footsteps are light not the heavy footsteps of the Doctor. After arguing for a time, the two of them resolve to break into Jekyll's laboratory. Inside, they find the body of Hyde wearing Jekyll's clothes and apparently dead from suicide. They find also a letter from Jekyll to Utterson promising to explain the entire mystery. Utterson takes the document home, where first he reads Lanyon’s letter and then Jekyll's. The first reveals that Lanyon’s deterioration and eventual death were caused by the shock of seeing Mr Hyde drink a serum, or potion, and as a result of doing so, metamorphose into Dr Jekyll. The second letter explains that Jekyll, seeking to separate his good side from his darker impulses, discovered a way to transform himself periodically into a creature free of conscience, this being Mr Hyde. The transformation was incomplete, however, in that it created a second, evil identity, but did not make the first identity purely good. At first, Jekyll reports, he delighted in becoming Hyde and rejoiced in the moral freedom that the creature possessed. Eventually, however, he found that he was turning into Hyde involuntarily in his sleep, even without taking the potion. At this point, Jekyll resolved to cease becoming Hyde. One night, however, the urge gripped him too strongly, and after the transformation he immediately rushed out and violently killed Sir Danvers Carew. Horrified, Jekyll tried more adamantly to stop the transformations, and for a time he proved successful by engaging in philanthropic work. At a park, he considers how good a person he has become as a result of his deeds (in comparison to others), believing himself redeemed. However, before he completes his line of thought, he looks down at his hands and realizes that he has suddenly once again become Mr Hyde. This was the first time that an involuntary metamorphosis had happened in waking hours. Far from his laboratory and hunted by the police as a murderer, Hyde needed Lanyon's help to get his potions and become Jekyll again; when he undertook the transformation in Lanyon's presence, the shock of the sight instigated Lanyon's deterioration and death. Meanwhile, Jekyll returned to his home, only to find himself ever more helpless and trapped as the transformations increased in frequency and necessitated even larger doses of potion in order to reverse them. It was the onset of one of these spontaneous metamorphoses that caused Jekyll to slam his laboratory window shut in the middle of his conversation with Enfield and Utterson. Eventually, the stock of ingredients from which Jekyll has been preparing the potion ran low, and subsequent batches prepared by Jekyll from renewed stocks of the ingredients failed to produce the transformation effected by the original potion. Jekyll speculates that the one essential ingredient that made the original potion work must have been a trace contaminant that was absent from the ingredients he had subsequently purchased. He assumes that subsequent supplies all lacked the essential ingredient that made the potion successful for his experiments. His ability to change back from Hyde into Jekyll has slowly vanished in consequence. Jekyll writes that even as he composes his letter he knows that he will soon become Hyde permanently, and he wonders if Hyde will face execution for his crimes or choose to kill himself. Jekyll notes that, in either case, the end of his letter marks the end of the life of Dr Jekyll. He ends the letter saying "I bring the life of that unhappy Henry Jekyll to an end". With these words, both the document and the novella come to a close.
