In this book, we hear how Gavroche was one of the Thénardiers' sons but was cast out into the street because his parents couldn't afford to feed or clothe him anymore.
As we might recall from earlier, Monsieur Gillenormand (Marius' grandfather) has a maid named Magnon whose two sons require the old man's financial support. One day, though, these sons die from an infectious disease. She doesn't want to give up the money, so she arranges to take two of the Thénardiers' sons and pass them off as her own.
Magnon eventually gets herself arrested while the two boys are out playing. They come home and find out that there's no longer any home for them there. A neighbor tells them what happened and gives them a piece of paper with an address written on it. But the paper blows out of their hands in the wind and they become lost. The two boys set out into the cold night to find shelter.
The two children eventually come into a barbershop and ask for help, but the barber violently chases them away. Gavroche sees the whole thing happen and offers to help the kids.
He buys them some bread, then he brings them inside a statue of a giant elephant (erected in memory of Napoleon). The whole thing is made of plaster and it makes for a cozy little home, even though the little kids are scared by how dark it is.
The only thing they really need to worry about are the rats, which can smell the flesh of young boys and are looking for a nibble…
Late in the night, the criminal Montparnasse comes to the elephant statue and tells Gavroche that his help is needed. Gavroche follows him and leaves the two young children to sleep soundly.
We find out that during this same night, Monsieur Thénardier and a couple of his criminal buddies have decided to break out of prison. The only problem is that after escaping the prison, Thénardier finds himself on top of a high wall that he can't climb down from. His only option is to wait until the prison guards find him and put him away for the rest of his life.
But have no fear, because here comes Gavroche. The young boy takes a length of rope and carries it up to Thénardier so that Thénardier can let himself down to the ground. While doing this, Gavroche recognizes Thénardier as his father, but neither of them seems too excited about it.
Little does Gavroche know that the two children he helped on this night are also his two brothers. How's that for a small world?