The story begins by introducing us to the character of the protagonist, Jemmy, who is a child who lives on the streets and in the sewers of the city of London. He and his father earn their living by capturing rats that they then sell on to people who own dogs that fight rats for entertainment. Because of the poverty in which he has grown up, it is clear that Jemmy is a character who is significantly more experienced and wiser than his years would suggest. In particular, the skills that he has picked up for independent living and self-reliance are very well honed.
Jemmy's life of course changes massively when he is taken from his harsh but contented life on the streets and moved into the royal courts. What happens then falls into the next section of the rising action of this excellent story. The exposition therefore introduces us to the main character and tells us something of his traits and the kind of life he has experienced, revealing to us the harshness of the poverty he has endured and how this has helped to mould Jemmy's character.