It is not difficult to create a sinister depiction of London as, naturally, fog rolls in so often, giving all who walk through it an eerie appearance. Then, too, the moon, Stevenson writes, shines much like a search light, illuminating only certain places and casting shadows. This scene certainly proves to be nightmarish as the moon that shines upon the kindly face of the gentleman soon reveals Mr. Hyde, who carries a heavy cane. Suddenly, he breaks into "a great flame of anger," brandishing the cane, and acting "like a madman." Then, Hyde, breaking "out of all bounds," beats the old gentleman with the cane, knocking the poor man to the ground in "ape-like fury." The maid is so horrified and frightened that she faints.
The shifting shadows created by light, fog, and followed by a wind that moves these shadows make for an eerie scene, indeed. In addition, the Soho area is a neighborhood that has inhabitants of rather unsavory character--"slatternly passengers," as the author describes them. The weather and the denizens of this area truly create what the author describes as "a district of some city in a nightmare."
Near the end of Chapter 4, Stevenson captures the scene and its tone with this description:
It was....the first fog of the season. A great chocolate-colored pall lowered over heaven, but the wind was continually charging and routing these embattled vapors....here it would be dark like the back-end of evening; and there would be a glow of a rich, lurid brown, like the light of some strange conflagration; and here, for a moment, the fog would be quite broken up, and a haggard shaft of daylight would glance in between the swirling wreaths.