This article confronts two serial novels, Les Mystères de Paris by Eugène Sue (1842) and the Portuguese “replica” of this matrix novel, Les Mystères du Limoeiro by João Cândido de Carvalho (1849). Through a cross-analysis of their incipits, considered as the opening moment of the novel, where the entry into the plot is played out and the reading pact is established, the article examines how the two narratives invite the reader to a journey into the underground worlds of the capital city, whereby reading becomes an adventure, and develop an imaginary topology of the urban depths.