Frederick and Rosanette have settled into a domestic routine. Translation: they're basically shacking up.
Her beauty has changed, and he admires her: "She wore on her face a continuous radiance, while at the same time she appeared more languishing in manner, more rounded in figure; and, without being able to explain in what way, he found her altered, nevertheless" (2.16.5).
Frederick hears some bad news about Arnoux. Turns out he has been keeping a woman from his factory who is clearly taking advantage of him. He seems to be getting a little senile.
The word is that Madame Arnoux is fed up with him, too. Arnoux visits Frederick to ask him to please come back and visit them again like he used to.
On the way to their house, Frederick is accosted by a strange man named Compain. He's talking about all sorts of characters and then asks Frederick if he's a member of "the calf's head." Frederick has no idea what he's talking about.
Frederick shows up at the house, but Arnoux isn't there. Madame is, natch, so he asks her why she never met him for their Tuesday afternoon rendezvous. She defends herself, telling him about Eugène's illness.
Sure enough, he's in love with her again and All is forgiven. Well then.
They fall into each other's arms, but just then, they hear a creaking noise. Someone is in the room: it's Rosanette. (Insert Psycho music).
Rosanette demands that Frederick leaves with her. A catfight almost breaks out, but things don't escalate too much.
At home, they get in a huge fight, and he tries to turn it on her, saying that she's been spying on him. Just as he's about to slap her, she announces that she's pregnant.
As you might imagine, this as a major obstacle to dumping her.
Meanwhile, Mademoiselle Vatnaz has been pressuring her to pay back a debt—which is why (she claims) she had shown up at Arnoux's.
Frederick goes to pay the debt himself. He finds Mademoiselle Vatnaz with Delmar and some others.
Frederick has had it up to here with Rosanette. Basically, he no longer finds her attractive. All she's good for is gossiping.
Frederick is pleased when the season of Madame Dambreuse's parties resume, and our boy is increasingly charmed by her. He spends a lot of time at their house; and occasionally on returning to Rosanette's house, he's pretty sure he sees men leaving. Looks like she's' up to her old tricks.
Frederick likes hanging out at the Dambreuse house for obvious reasons: they're wealthy and well-connected. Of course, the conversation can be annoyingly obsessed with politics.
Our protagonist is determined to make Madame Dambreuse his mistress; He doesn't love her like he does Madame Arnoux, and he doesn't lust for her like he does for Rosanette, but she has a certain something. What's that something? Aristocracy.
One day, the lady relents to his charms. Success!
On his way home, he runs into Deslauriers, who has been personally defeated by his failures: neither the Conservatives nor the Socialists will have him.
Frederick invites him to stay at home and sleep in his bed, explaining that he "has others." Deslauriers tries to pry, but Frederick basically tells him to mind his own beeswax. Deslauriers also urges Frederick to run for Assembly again.
Frederick finally enjoys a delightful and romantic dinner alone with Madame Dambreuse, and when he returns to Rosanette that night, she's psyched to see him. And Frederick is psyched to be himself.