The story of Dr Jekyll’s scientific experimentation and his eventual downfall is told for the first eight chapters from the point of view of his friend, Utterson. In the ninth chapter, Dr Lanyon tells his version of the events and, in the final chapter, Jekyll gives the reader his own personal account of the story.

Utterson is introduced. His friend, Richard Enfield, relates a story of how he saw a strange, dreadful man named Hyde trample over a little girl. When forced to pay off the girl’s family, Hyde went through a shabby-looking door to collect the money.

Dr Jekyll is Utterson’s friend. Jekyll has written a strange will in which he leaves all of his wealth to the strange Mr Hyde. Utterson is uneasy about this will and visits a mutual friend, Dr Lanyon. Dr Lanyon states that he has had an argument with Jekyll over scientific theories and experiments. Utterson returns to the shabby door and waits there until he meets Hyde. Hyde fills him with horror.

Utterson visits Jekyll to discuss the will. Jekyll refuses to talk about it or to change the will.

The story moves on one year. Hyde murders an elderly gentleman, Sir Danvers Carew, in the street by beating him to death with a walking stick. Utterson identifies the body and the walking stick, leading the police to Hyde’s house. The house is empty and Hyde is gone.

Later that day, Utterson visits Jekyll who is sick and miserable. Jekyll promises Utterson that he will never see Hyde again, showing him a letter written by Hyde which states that Hyde has escaped. Utterson suspects that the letter is a forgery and that Jekyll has written the letter, pretending to be Hyde.

Three months pass. Jekyll seems better and there is a dinner party where Lanyon, Utterson and Jekyll all meet as great friends. However, a few days later, Jekyll refuses to see anyone. Utterson visits Lanyon and is horrified to find Lanyon a changed man. He is very sick and puts the blame for his illness on a dreadful shock. Shortly afterwards, Lanyon dies, leaving a letter for Utterson to read if Jekyll ever disappears or dies.

Utterson and Enfield pass Jekyll’s house while on one of their weekly walks. Jekyll is sitting in his window, too sick to come outside. As they speak, Jekyll’s face is contorted with horror and he swiftly closes the window.

Utterson is summoned by Jekyll’s butler, Poole, to come and help at Jekyll’s house. Jekyll has shut himself completely away in his cabinet and the servants are terrified by the strange sounds coming from behind the locked door. Utterson and the servants break down the door to find the dead body of Hyde. He has committed suicide by taking poison. There is no sign of Jekyll but there is a new will and a letter or statement from Jekyll. Utterson returns home to read the letter from Dr Lanyon and also read Jekyll’s statement.

In the letter, Dr Lanyon relates his story of how he received a written note from Jekyll begging for help. Lanyon responded and did as Jekyll requested, collecting a drawer of chemical powders from his laboratory. That night, Hyde appeared and Lanyon, as instructed, handed over the chemicals. Hyde mixed these into a potion and drank it, transforming into Jekyll. The shock of this made Lanyon fatally ill.

Jekyll tells his own story in his statement, sharing with Utterson how he had always felt as if there were two sides to him. His scientific studies led him to devise a potion which could turn him into the ‘bad’ part of himself; this potion caused him to change appearance so that he became Mr Hyde. As Mr Hyde, Jekyll explored his darker side and became increasingly violent until he ended up murdering the elderly man, Sir Danvers Carew. After this murder, Jekyll stopped taking the potion but found himself changing into Mr Hyde anyway. Jekyll ran out of the potion that he needed to transform back and so wrote his statement for Utterson, explaining what had happened,. Then he prepared to die, fatally weakened by the effects of the potion.