Peter Harris is a middle aged, married (to Rebecca), New York art dealer who leads the sort of life that many would envy. Of course it is not perfect. Who among us has a perfect life? His marriage provides the sort of comfort that comes with time although the flip side of that is a lack of rip roaring excitement. His college age daughter appears to hate him, perhaps because she is not beautiful and he has let her know he thinks so. But she lives in Boston and Peter is able to put her out of his thoughts most of the time. On the whole he is semi-satisfied but there is something missing. Then his wife's lookalike, drug troubled, much younger brother arrives on the scene. He finds himself attracted to Mizzy (short for "The Mistake") and this is the Death In Venice crux of the novel.
I enjoy Cunningham's writing and I liked this book - it was perfect for a transatlantic flight because it is slim and could be devoured in one go. It describes continuums of happiness that most of us experience (if we are lucky). In this novel Peter is at the low point in this continuum.
Cunningham is a gifted writer and I liked By Nightfall but I felt there was something troubling about the story. I ended up shaking my head after reading it. I don't find it odd that a heterosexual guy involved in the New York art scene would be attracted to his brother-in-law. But the fact that he met said brother in-law when he was a little boy and that he had acted as a mentor to the boy make the attraction creepy a la Woody Allen.