Hugo opens Book Three of Les Misérables by discussing the street children of Paris and going through all of the different "types" of urchins as though they were sub-species of humanity. When he's done with that, he gives a long discussion of Paris as though the city were a sort of person with a specific personality.
The book turns its attention to a Paris urchin named Gavroche. According to the book, Gavroche always has a smile on his lips, but his heart is dark and empty.
Gavroche goes to visit his family sometimes, and his family lives in the same apartment building that Jean Valjean used to live in. Unfortunately, Gavroche's family dislikes him and does nothing for him, even though he's just a little boy.
Down the hall from Gavroche's family lives a penniless young man named Marius, who is the book's main man. Don't worry, though. You'll find out soon enough why the book has given you a description of Gavroche and his family.