Task: Question Generation
Input (English):  The Mystery of a Hansom Cab takes place in Melbourne, Australia and involves an investigation into a homicide, after a corpse is discovered in the evening, in a hansom cab. The city of Melbourne plays a significant role in the plot and, as the author describes: "Over all the great city hung a cloud of smoke like a pall." The killer's identity is not as significant a revelation in the story as are the roles of the influential and secretive Frettlby family, and their secret: they have an illegitimate daughter living on the streets. The class divide between Melbourne's wealthy and less fortunate is addressed throughout the plot.
The protagonist in the novel is a policeman named Detective Gorby, who is given the task of solving the murder. As Hume describes the character's investigative skills: "He looked keenly round the room, and his estimate of the dead man's character was formed at once." The author commented in a later introduction, "All of the scenes in the book, especially the slums, are described from personal observation; and I passed a great many nights in Little Bourke Street, gathering material". At this time, the street had gained notoriety as a place frequented by prostitutes and criminals.
Output (English): What covered the city?