The writer Robert Louis Stevenson is lying feverishly in bed at night, hallucinating. He begins to imagine the tale of a good doctor who turns into his evil twin.
Dr. Jekyll is trying to demonstrate the idea of dual personality to a group of wealthy donors in a mental asylum. Failing to convince the crowd of the efficacy of his ideas, Jekyll returns to the privacy of his own laboratory for further experimentation, frenetically pursuing his goal of unearthing the hidden underbelly of the human experience. He feels a premonition of Mr. Hyde, the repressed force of evil whom Jekyll is trying to unleash. To resist the pull of Mr. Hyde, Dr. Jekyll attends a party at Sir Danvers Carew, whose daughter Nellie he is engaged to. As the party draws to a close, the gentlemen guests decide to finish the evening at Deacon Brodie’s Tavern, an underworld den of prostitutes, lowlifes, and drugs. Jekyll begins to shed his proper demeanor and come alive, as we sense his “other self” emerging. Propelled back out onto the city streets, Jekyll begins to transform before our eyes. The effects are immediate and startling: nightmare versions of characters we have already encountered begin to appear. At the climax of Jekyll’s hallucination, Mr. Hyde emerges triumphantly from the shadows.
In an elegant ballroom, Sir Danvers Carew is giving a party. Mr. Hyde appears, engaging provocatively with the guests. Fearing that the effects of the potion are about to wear off, Hyde escapes back to the streets, where he collides with a small child. In his rage and panic, Hyde beats the child to death with his cane. Back at his lab, Hyde struggles to resist returning to the body and mind of Dr. Jekyll. The terrifying figures of hallucination return.
Dr. Jekyll, isolating himself from the public eye and frightened about where his “research” is taking him, returns to his experiments in the lab. Friends and colleagues come to visit but Jekyll resists seeing them. Finally at Dr. Lanyon’s insistence, Jekyll consumes the dangerous potion in front of them, transforming into the raging Mr. Hyde. Violence and destruction ensue as Hyde attacks his former friends and destroys Dr. Lanyon, Sir Danvers Carew, and Rowena, a prostitute at the tavern. When Nellie Carew goes to Dr. Jekyll’s house out of concern for the doctor she has loved, her encounter becomes more and more violent until Hyde tells her to “RUN!” and she escapes. In the empty lab, Dr. Jekyll and Mr. Hyde battle with each other for dominance and survival. Stevenson reappears, and all of this has been happening in his feverish imagination. The world of the mental hospital returns, as Stevenson realizes that in writing the story of The Strange Case of Dr. Jekyll and Mr. Hyde, he has unleashed a monster into the world, the dark side of all of our better selves.