A bit of trivia from Edith Wharton Society: the title (The House of Mirth)...is taken from Ecclesiastes 7:4: "The heart of the wise is in the house of mourning; but the heart of fools is in the house of mirth."
Here is my summary of Book One without too many spoilers:
Main character, Lily Bart, 29, beautiful, single, and "poor," lives with her rich aunt in New York and desperately wants to avoid living a single, independent, and dingy life, "like a pig." She must marry well.
When she was 19, her father financially ruined the family before he died, leaving Lily and her mother with nothing. Her mother loathed poverty and hoped Lily's beauty would enable her to marry into wealth. When her mother dies, Lily's Aunt Julia takes her in.
Lily's beauty, family connections to wealth, and her aunt's generosity enable Lily entrance into prominent social circles in New York. She pursues a handsome, rich bachelor named Percy Gryce, though he is extremely boring. Such is the price Lily would have to pay if she never wants to worry about money. To her benefit, Mr. Gryce is interested in her, and there may have been a deal had Lily not ruined it by putting him off. Why did she let him slip away?
Lily has a fascinating friend, Lawrence Selden, who makes a decent living because he works hard for it; but unlike those in high society, Lawrence does not care about money. He and Lily are like opposites: to Lily, success is getting what you can out of life; to Lawrence, success is personal freedom - "to keep a republic of the spirit." With Lawrence, Lily can be herself. He knows her better than she knows herself, and they work well together. He loves Lily, yet she will not reciprocate.
Since Lily is not honest with others in high society, she gets into uncompromising situations because of her deceitfulness or fear of truth. She lies to Mr. Rosedale, an extremely wealthy and powerful social climber, about being with Lawrence, which she later regrets because she knows he is going to spread rumors about her. She gains financial help from Gus Trenor, her friend's husband, while he continuously pursues Lily in return for romantic favors. How long will it be until she tells him no and reminds him that he is married? She also lies to her aunt about how much money she owes, to whom, and why.
Numerous complications occur for Lily as she digs a hole for herself that she cannot get out of. But why does she keep going back to that circle of society? Lawrence warns her: "the things she desires will not make her happy. In fact, she really hates them." If only she could see how content she would be if she would admit that Lawrence is the best life for her. But, no!
The night that Lily ends up in a dangerous situation with an angry Gus Trenor and escapes just in time, Lawrence witnesses her leaving. He gets the wrong idea and is hurt; all the ideas about her having an affair with Trenor must be true.
At the end of Book One, Lily expects to meet with Lawrence the next day, but he never shows. Brokenhearted, he leaves the States without even sending her a note goodbye.
To continue reading, see Book Two summary.