Flashback time! Hugo starts this part of the novel with a painstakingly detailed account of the Battle of Waterloo, which is basically the battle that ended the military career of Napoleon Bonaparte and his furious conquering of Europe.
For much of the battle, it looks as though Napoleon is going to be victorious. But then the Prussians show up and put Napoleon and his men on the run. (Brain snack: Prussia existed back in the 19th century and included most of present-day Germany.)
And now we look in on all the dead bodies lying around the battlefield. Among these bodies, there's a night prowler wandering around. As he scurries about, he sees a hand sticking out from a pile of bodies and catches the glimmer of a gold ring on one of the fingers. He snags the ring off the man's finger, but when he turns, he finds that the hand he robbed is now holding on to him. It's alive!!!
The prowler turns around and pulls the wounded man's body out of the pile in order to rob him of more stuff, but the wounded man thinks that the prowler is saving his life. He thanks the prowler for his help and asks for his name. The prowler replies that his name is Thénardier. Gasp!
The wounded man replies that his name is Pontmercy and that he'll never forget that Thénardier saved his life. Thénardier doesn't bother to correct him on that one.