Mrs. Trenor berates Lily for being completely flaky and indecisive. Because Lily took Selden away from Bertha, Bertha retaliated and turned Percy against Lily by giving him all the dirt on her. She told him how Lily gambles, smokes, and doesn't go to church.
Now, Percy has left Bellomont, essentially to run away from Lily.
It takes a while, but Lily finally realizes how screwed she is.
At lunch, Lily discovers that Selden has departed from Bellomont, in addition to Percy.
Mrs. Dorset is there, playing nice on the surface, but obviously mean underneath. She's all, "Oooh, Lily, I wonder why Mr. Gryce isn't here anymore! How curious!" and that sort of thing.
Lily suffers inwardly at the thought of the rich life she just lost.
As Lily heads away from the table, Mrs. Trenor asks her to go to the station and pick up her husband, Gus Trenor, and bring him back to Bellomont. She said she would send Carry Fisher, but she knows that Mrs. Fisher is always trying to get money out of Gus.
On the way to the station, Lily devises a plan to get out of her hidden debt with the help of Gus Trenor. Of course, Lily knows that a married woman can do things (like borrow money) that a single girl cannot (because of the implications that favors were traded for the cash). She decides that she'll have to tread carefully.
Gus Trenor is "red and massive." Lily is well aware of the fact that he finds her attractive.
Trenor starts talking about his work. He admits to Lily that it takes a lot of time (and causes him a great deal of stress) to keep Judy in the lifestyle they live. (He's in the stock market.)
He also says that he's made a good deal of money trading on tips from Simon Rosedale – he wishes his wife would stop being so snobbish and invite Rosedale to dinner, since he's such a useful business acquaintance to have.
Lily realizes this is the angle she can work. When they arrive at Bellomont, she asks Trenor to keep driving, so they can enjoy this nice little carriage ride together a bit more.
Lily starts lamenting how awful her financial situation is, how she can't play bridge anymore and can't buy such pretty dresses, etc. She asks for Trenor's help in explaining to Judy that Lily can't stay with them as she does. She needs to go back to her aunt's, where the social pressure to spend money all the time isn't there.
This touches Trenor. He hates the thought of the beautiful Lily Bart having to do without. He asks for her to give him the small amount of money she has – about 500 dollars – and let him speculate with it on the stock market.
Lily is relieved, and exhilarated with the sense of her own power.