All of the characters in this sound clever and interesting, which helps to make this story quite engaging. It's all very traditional, with diaries, and letters, and notebooks, and self-reflection and the recounting of one's thoughts and history.
The crux of the story is Iris Chapel and her wish to escape her multi-millionaire family and its unsavory origins. The book goes into pretty fine detail about her character, her upbringing, her experiences. It's a little odd in that Irish Chapel is a product of the mid-twentieth century. You'd think that the fortune was old-money enough and her life modern enough that the fortune's past wouldn't trouble her so, and she could move on or change her name or live a different life and not be haunted by the past.. It's all clearly based on the story of the Winchester fortune.
It's not quite a comedy of manners, but it's a literary study of manners and mores that Edith Wharton might have approved of, with wonderful attention to the surface details of a gracious, privileged existence. It's the sort of book that Huguette Clark might have written had she not lived such an empty, doll-collecting existence.