Julien finishes putting together the anonymous letter for Madame de Rênal and hands it to her. In return, she hands him a box with gold and diamonds in it and asks him to bury it in the mountains. She's afraid that someday she might need it if she's kicked out of her home.
Meanwhile, Monsieur Rênal stresses about how to bring up the letter he has received with his wife. It's clear that the letter has told him about his wife's affair.
The whole thing makes de Rênal think about how many men dislike him and how few like him. He even thinks about friends whom he cut ties with when he was younger because they weren't upper class enough.
He thinks about beating up Julien and throwing him out of the house. But he knows that this would eventually cause the scandal to become known to everyone in town. He can't stand the thought of having the newspapers drag his name through the mud.
Madame de Rênal comes up to him with a devastated look on her face. She hands him a letter and says someone from town she didn't recognize just gave it to her. She asks Monsieur to send Julien back to his father as quickly as possible.
Monsieur de Rênal tells her to stop being an idiot. She waits patiently for him to get all his anger out of his system.
Madame plants the suspicion in her husband's head that it is actually the servant Elisa and Valenod who are having an affair. She also tells him that Mr. Valenod has written her (Madame) many love letters over the years. She shows them to her husband, and this proves that Valenod has a motive for trying to ruin Madame's reputation.
The next step is for Madame to convince Monsieur never to confront Valenod about the letters (since he could always tell Monsieur the truth about which letters have come from him and which ones haven't).
Madame demands that her husband send Julien away for at least a couple of weeks. He agrees.
With all that's happened, Madame still asks Julien to come to her room that night. He thinks she's insane. But of course he comes.