The party at the apartment includes many different characters.
Tom takes Nick there.
Tom is definitely upper class.
Nick is certainly middle class, he has a job, and a place that meets his needs comfortably, but not excessively.
Myrtle, Tom's mistress, is married to a garage mechanic and owner. This man is likely middle class, but certainly feels lower class because it is a dirty profession. This makes her middle class.
Mr. and Mrs. McKee go to the party and they live in the building where Tom and Myrtle get away together. They are a couple that does photography. They could be considered middle class.
Lastly, Catherine, Myrtle's sister is probably middle class too.
The irony of this party is that all of these middle class folks would like to make it appear that they are upper. This is pretty indicative of the era, always longing for more...
- There's Tom: the upper class, or bourgeoisie, the established rich, the very wealthy, the capitalist class.
- Nick: the middle class, the petty bourgeoisie, the small business proprietor, the semi-wealthy.
- Myrtle & Katherine: the lower class, the proletariat, the working class (even though they don't work; Myrtle is defined by her husband's work).
Myrtle, in her time in New York, actually jumps classes, moving from the proletariat to the bourgeoisie temporarily. Her dream is obviously to stay there. As Tom's mistress, she is queen of the apartment. She has a dog with a fancy collar, signs of frivolous spending and disposable income.