People refer to this as Wharton's most erotic book. I disagree with that characterization - I think that The Age of Innocence, with its unrequited, simmering passion between Countess Olenska and Newland Archer is much more erotic. This one is sexier.
Charity Royall is a young woman who has been raised by Lawyer Royall in North Dormer, a small New England town. Her family comes from the mountain, a poverty-stricken area. At some point, Lawyer Royall finds himself attracted to the young woman and proposes to marry her. This is squicky as all hell, since he has basically been her father since she was a small child.
Charity understandably turns him down, being attracted to Lucius Harney, man about town, photographer, and the nephew of another one of New Dormer's finest citizens. He is clearly above her in social position. Charity, recklessly, falls for him, and the two of them embark on a sexual relationship. This is a Wharton book, however, which means that the reader pretty much has to guess what has happened.
It isn't just the lack of explicit sex that wasn't erotic. It was the shallowness of the connection between Charity and Lucius Harney. There is no reason to believe that Harney wasn't absolute rubbish as a lover, self-absorbed and concerned with neither Charity's pleasure, nor her plight. (Did I just accuse a fictional character of being crap in bed. Why yes, yes I did. And I stand by the accusation. There is no chance that poor Charity had an orgasm. None at all.) It is easy to sympathize with Charity, and to deplore her poor choices, but it was so obvious that Harney was just exploiting her, and it made me want to shake her.
Wharton's books explore the border between social expectation and human agency. I have read three of them - The House of Mirth, The Age of Innocence, and now Summer, and all of them consistently decry the way in which individuals, especially women, but not only women, are oppressed by society. She lived in a time when the social customs were extremely restrictive - people behaved in specific, rote ways, dependent upon their social classes, and the upper classes, in particular, were required to maintain certain standards that were very limiting. Wharton's books explore what happens when the individual steps outside of those lines.
Usually, it is pretty much a disaster. In this book, actually, Charity managed to pull out a win for herself. While the twenty-first-century independent romantic in me was pretty much completely grossed out by the way it ended, by 1917 standards, Charity does pretty well, with a solid, middle-class existence. She fared a lot better than Lily Bart, from The House of Mirth. Interestingly, she doesn't share Lily Bart's honorable qualities. That's probably sort of the point - when hunger conflicts with honor, hunger must, and usually will, win. Or, you die.
Anyway, Wharton is depressing as hell, but always worth reading.