As I understand this, Denham and Katherine are the youngest people in the room, by far - and moreover, Denham is an outsider in the group, and Katherine is only there because she's the daughter of one of the older people - so they can't really join in the conversation easily with these older folks. If you're a non-native speaker and you're reading this for pleasure, you've picked a bear of a book. This is difficult reading.
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