The Strange Case of Dr. Jekyll and Mr. Hyde, by Robert Louis Stevenson, is a novella published in the 1880s that deals with the duality of human nature. The story is told from the point of view of Mr. Gabriel John Utterson. Utterson is a lawyer and friend of Dr. Jekyll’s. The book opens with Utterson walking and conversing with Mr. Enfield, who is a businessman and distant cousin. Mr. Enfield recounts to Mr. Utterson how he once saw a man named Hyde, who had run over a girl, come out of a door they are passing, with a check signed by Dr. Jekyll. The check was for almost one hundred pounds. Utterson notes that the door in question leads to a laboratory that connects to his friend’s, Jekyll’s, house.

Utterson returns home after his walk with Mr. Enfield and goes straight to his study, where he has a copy of Dr. Jekyll’s will. The will stipulates that should Jekyll disappear or perish, Edward Hyde will inherit his estate. Certain that there is something wrong, that Dr. Jekyll must have been in some way tricked or coerced, Utterson visits his friend to inquire about his beneficiary. Dr. Jekyll not only assures Mr. Utterson that his will is correct and he intends to pass on everything to Hyde, but he also refuses to talk about his connection to Hyde, which vexes Mr. Utterson.

About a year passes, and a maid witnesses a crime while looking out her window. She sees a man attack another, elderly man, killing him with a club. She recognizes the murderer; it is Edward Hyde. His victim was a man named Sir Danvers Carew, a respected gentleman and one of Mr. Utterson’s legal clients. Following the gruesome murder, Utterson goes with the police inspector to look for Hyde, who reportedly lives in Soho, then a seedy area of London. However, they can’t find Edward Hyde. With Hyde missing and suspected of murder, Mr. Utterson worries for Dr. Jekyll’s safety. He goes to his friend and asks again after his connection to Edward Hyde. Once more, Dr. Jekyll will not go into detail, but promises that he won’t have dealings with Hyde anymore. He shows Mr. Utterson a letter from Edward Hyde, promising that he won’t hurt Dr. Jekyll. Mollified, Mr. Utterson lets the matter drop.

For a while, everything seems as it should be. Dr. Jekyll hosts parties and works with charities, and there is no more mention of Edward Hyde. Then, a close friend of Jekyll’s and Utterson’s suddenly falls ill. His name is Dr. Lanyon. Mr. Utterson pays him a visit, but Lanyon flatly refuses to discuss anything related to Dr. Jekyll. Instead, he hands Mr. Utterson a letter with instructions that it not be opened until after he has died. Dr. Lanyon dies a week after he gives Mr. Utterson the letter.

Before Utterson can read the letter, he and Mr. Enfield witness a shocking event. While out on another walk, they come across Dr. Jekyll’s home. He talks with them out his window, but then he transforms, which shocks them both. It’s not until Mr. Utterson goes into Jekyll's laboratory after hearing Hyde’s voice that he confirms the truth: inside, he finds Edward Hyde, dead on the floor and wearing Dr. Jekyll's clothes. He finds a letter on the body from Dr. Jekyll.

Mr. Utterson reads Dr. Lanyon's letter first. Lanyon explains that Dr. Jekyll had been having difficulties with the side effects of a drug he was working on, and that he had asked for Lanyon’s help in procuring some hard-to-come-by ingredients for it. Lanyon describes how Dr. Jekyll transformed into Edward Hyde, and how that transformation shocked him into his sickness and ultimate death. Mr. Utterson, continuing to read Dr. Jekyll’s letter, discovers that the drug he was working on was meant to test whether or not man had a dual nature—good and evil. With the drug, he could separate out his evil side, embodied by Edward Hyde. Unfortunately, the more Dr. Jekyll worked with the drug, the less predictable it was, so that he could no longer control when he turned into Edward Hyde or what Hyde would do when in control. He knew that if Hyde won, he’d cease to be Dr. Jekyll, and all of his goodness would be gone. So, he wrote the letter and took his own life.

Literature during the Victorian era often sought to determine what makes human nature what it is. Madness, one’s own capacity for good versus evil, and playing God often wove their way into written works of the time. The Strange Case of Dr. Jekyll and Mr. Hyde examines all three of those themes, and was so well-received that the story has become a part of popular culture and the modern vernacular.