The Underground Man launches right back into his "life's a b---h and then you die" speech. He says he's essentially disgusted with Liza's occupation, but if she were something else, he might very well fall in love with her.
As such, though, he could never love her, because she's just a slave who has to come when he calls. Even the lowest of workmen, he says, isn't a slave.
He adds that Liza isn't selling just her body, she's in fact selling her soul, which she has no right to do.
A maiden's treasure, he says, is her love. It's as valuable as a diamond, and a man will do anything to get it. But if she gives away sex without love, why would man strive for her love?
In fact, he tells her, not only do men not love her, but they don't respect her, and they laugh at her.
If she doesn't believe him, all she has to do is ask one of her clients if he will marry her. When he laughs in her face, it should be proof enough.
The Underground Man adds that she can't rely on her youth and good looks, since those will fade fast.
He tells her of yet another woman he's seen recently, probably a former prostitute, who was drunk and homeless and kept getting beat up.
No, he's not done yet. The Underground Man, after detailing the horrible disease which Liza will probably contract, adds that everyone will yell at her for taking too long to die and for being a burden while she's sick.
And after that, when she finally does die, no one will care and no one will come to her funeral, and no one will ever miss her or even remember her name.
And then…he stops talking. He's nervous; he knows he is talking "like a book," as she said, but he also realizes that he's had a huge effect on Liza. She's thrust her face into her pillow and is grasping at it with both hands.
He feels bad, so he takes her hands and tells her that he's sorry and he didn't mean it. He also gives her his address and tells her to come and see him. She agrees.
Then the Underground Man feels awkward and decides he needs to get away. Before he can escape, however, Liza tells him to "wait a minute" while she rushes to another room. She returns with a letter in her hand and shows it to him.
It is a love letter, and a very chaste, respectful one at that.
Liza explains quickly that she was at a party and met a boy who didn't know she was a prostitute. He fell in love with her there – hence the letter.
The Underground Man realizes what's up: she wants him to know that there is a man somewhere who loves her. And even though Liza knows this love will never come to fruition, she can at least keep the letter as "a precious treasure."
The Underground Man knows he has to get away immediately, since he has just become aware of a "loathsome truth."