On their weekly walk, an eminently sensible, trustworthy lawyer named Mr. Utterson listens as his friend Enfield tells a gruesome tale of assault. The tale describes a sinister figure named Mr. Hyde who tramples a young girl, disappears into a door on the street, and reemerges to pay off her relatives with a check signed by a respectable gentleman. Since both Utterson and Enfield disapprove of gossip, they agree to speak no further of the matter. It happens, however, that one of Utterson's clients and close friends, Dr. Jekyll, has written a will transferring all of his property to this same Mr. Hyde. Soon, Utterson begins having dreams in which a faceless figure stalks through a nightmarish version of London.

Puzzled, the lawyer visits Jekyll and their mutual friend Dr. Lanyon to try to learn more. Lanyon reports that he no longer sees much of Jekyll since they had a dispute over the course of Jekyll's research, which Lanyon calls "unscientific balderdash." Curious, Utterson stakes out a building that Hyde visits—which, it turns out, is a laboratory attached to the back of Jekyll's home. Encountering Hyde, Utterson is amazed by how undefinably ugly the man seems as if deformed, though Utterson cannot say exactly how. Much to Utterson's surprise, Hyde willingly offers Utterson his address. Jekyll tells Utterson not to concern himself with the matter of Hyde.

A year passes uneventfully. Then, one night, a servant girl witnesses Hyde brutally beat to death an old man named Sir Danvers Carew, a member of Parliament and a client of Utterson. The police contact Utterson, and Utterson suspects Hyde as the murderer. He leads the officers to Hyde's apartment, feeling a sense of foreboding amid the eerie weather—the morning is dark and wreathed in fog. When they arrive at the apartment, the murderer has vanished, and police searches prove futile.