Mr. Utterson is a London lawyer who is a friend of Dr. Jekyll. Jekyll gave up his regular practice to experiment with non-traditional medicine. Utterson is concerned because Jekyll has written a will that leaves all his money to his new partner Mr. Hyde. Utterson has heard bad things of Hyde and disliked him at first sight. The lawyer thinks his friend is being blackmailed.

One day, the lawyer is asked to identify the body of a murdered man, Sir Danvers Carew, one of Utterson’s clients. Hyde is suspected of the murder, but he has disappeared. Jekyll swears that he has not seen Hyde and has broken with him forever. The case remains unsolved and Jekyll becomes more sociable than he had been.

Suddenly, though, he locks himself into his laboratory, yelling to the servants through the door, directing them to gather chemicals for him. The servants recognize a change in his voice and think that their master has been murdered; another man has taken his place in the lab. They call Utterson who breaks down the door. On the floor lies Hyde, who has killed himself with poison. Sadly, Utterson assumes Hyde returned and killed Jekyll, but the doctor’s body is nowhere to be found.

He does find, however, a letter in which Jekyll explains his relationship to Hyde. Jekyll had sometimes indulged in debauches which, if discovered, could have ruined his reputation and of which he is ashamed. Pondering this split in his personality, he decides to find a way to separate his two beings. Jekyll creates a potion that releases his evil side, Mr. Hyde. Hyde is shorter and smaller than Jekyll, having not had as much exercise.

For a while Jekyll enjoys his two bodies; he can do whatever he likes without fear of discovery. His pleasure is stunted when Hyde kills Carew in a nonsensical fit, and he resolves never to take the potion again. Hyde is now strong, however, and emerges whether Jekyll will have him or not. Indeed, Jekyll must use the potion to be rid of him if only for a moment. Jekyll knows that it is only by killing his body that Hyde’s body, too, will die.