"before the era of reconstruction dawned upon London"

Over London by Rail by Gustave Doré (1870)
Public DomainOver London by Rail by Gustave Doré (1870)

Between 1831 and 1925, London was the largest city in the world. The decline of manual techniques in agriculture after the Industrial Revolution, combined with the burgeoning opportunities in factories around the capital, brought hundreds of thousands of people to the city, necessitating a flurry of construction to house them all. The house in which the Verlocs live was built before this rush and so by 1886, when the story takes place, it would have been quite run down and grimy, smeared with soot from the city factories.