Most good stories start with a fundamental list of ingredients: the initial situation, conflict, complication, climax, suspense, denouement, and conclusion. Great writers sometimes shake up the recipe and add some spice.
Since The House of Mirth was published, critics have been complaining about its lack of conventional plot structure. Basically, the novel is more a series of episodes than it is a seven-part Classic Plot. You could see each episode as being its own little climax, suspense, and denouement.
Take, for example, the big scandal in Monte Carlo. Initially, Lily, George, Bertha, and Ned are all out for the night. Conflict begins when Bertha and Ned are nowhere to be found and George and Lily return alone. Complications rise the next morning, when George informs Lily that Bertha didn't come back until 7am; he suspects an affair. We get the climax when Bertha, alone with Lily, blames her for the scandal. Suspense rules the scene during dinner, when Lily and Selden anxiously wonder what's going to happen between the Dorsets, and denouement is the name of the game once Bertha kicks Lily off the yacht.
You could run this same classic plot through for any of the other episodes in House of Mirth, from Lily's attempt to marry Gryce at Bellomont (climax is her decision to skip church and take a walk with Selden) to her stint as a secretary for Mrs. Norma Hatch (climax occurs when Selden pays her a visit and begs her to leave). OK, now you can try analyzing a few scenes on your own.