Robert Louis Stevenson said that the plot of The Strange Case of Dr. Jekyll and Mr. Hyde (first published without “The” as the first word in the title) first came to him in a nightmare and that, after waking up, he wrote the first draft in three days. Stevenson introduces the mystery of the evil Mr. Edward Hyde—the central puzzle of the story—early in the novel, but he does not provide a solution to the mystery until the very end. The reader’s first encounter with Hyde is at second hand, in a story told to Gabriel John Utterson, a lawyer friend of Dr. Henry Jekyll, by Richard Enfield, who saw Hyde trample a child. Because Jekyll recently has changed his will to leave all of his money to Hyde, Utterson is intrigued and begins to investigate. He fears that Hyde is blackmailing Jekyll and plans to murder him.
When Sir Danvers Carew, a respected member of Parliament, is murdered and Hyde is implicated by a witness, a manhunt begins, but Hyde cannot be found. Utterson begins to suspect that more than a murder is involved when he discovers that the handwriting of Jekyll is identical to that of Hyde, except for the slant of the letters. His suspicions deepen when he learns that Dr. Hastie Lanyon has developed hard feelings toward his old friend, Henry Jekyll. Although Lanyon is dying, he refuses to see Jekyll again.
The mystery that surrounds the relationship between Jekyll and Hyde is revealed gradually by means of a letter from Lanyon that is to be read by Utterson after Lanyon has died; however, Lanyon’s letter contains another letter that is not to be opened until the death or disappearance of Jekyll. When Poole, Jekyll’s butler, tells Utterson that Jekyll has disappeared and that Hyde is locked in Jekyll’s laboratory, Utterson and Poole break down the door. They find only the body of Hyde and a note from Jekyll requesting that Utterson read Lanyon’s letter.
The letter recounts a request by Jekyll to bring some chemicals to him. Hyde appears in Jekyll’s laboratory, and Lanyon sees Hyde swallow the chemicals and become transformed into Jekyll. The shock of witnessing the transformation apparently hastened Lanyon’s death. When Utterson opens the accompanying letter, from Jekyll, he discovers that Jekyll has been obsessed with a theory of the duality of good and evil in all human beings and that he has discovered a formula that transforms him into his evil side. When he begins to change into Hyde without the chemicals, however, Jekyll despairs, for after he exhausts his supply of chemicals he can no longer transform himself back. As he completes the letter, he changes back to Hyde the last time and kills himself.