On the surface, By Nightfall, the latest novel from Pulitzer Prize novelist Michael Cunningham (The Hours, A Home at the End of the World), might seem like a typical narrative about dull people leading dull lives. But beneath the seemingly placid lives of wealthy Manhattanites Peter and Rebecca Harris, the author has created a story that’s anything but dull.

While the 40-something Harrises seem happy at the outset, it soon becomes clear that Peter, at least, is leading a life of quiet desperation. A successful but unfulfilled art dealer, he loves his wife, but it takes the arrival of her much younger brother Ethan (an unplanned child known to his family as “Mizzy,” which is short for mistake) to stay with them to reawaken his long lost sense of passion.

Mizzy, a former drug addict with vague hopes of doing “something in the arts,” doesn’t seem like someone to envy, but Peter is nonetheless entranced by his youth and beauty, and the memories it stirs in him of both a younger Rebecca (whom her brother resembles),and his own younger, freer self.

Mizzy, for his part, wouldn’t ordinarily care much about Peter, but has to pay attention to him after he invites a dealer to the couple’s apartment one afternoon to buy a gram of cocaine and later realizes his brother-in-law, home sick in bed, overheard the whole transaction.

While this is essentially the inciting incident, By Nightfall has no plot in the typical sense. Much of the action is psychological rather than physical, and Cunningham relates Peter’s struggle to understand the feelings Mizzy has aroused in him in a rambling stream of consciousness style. This certainly could have been boring, but Peter, a wryly neurotic and sympathetic if not immediately likable character, is in fact quite humorous and compelling, even when doing little.

Though the book’s inside cover describes it as “full of shocks and aftershocks,” this is a bit of a stretch that’s also quite unnecessary. One of Cunningham’s strengths is his ability to describe surprising events without seeming melodramatic. When relations between Peter and Mizzy take an unexpected turn, for instance, he writes only: “And then, it seems, they are kissing.” Later on, when Peter tries to persuade Rebecca to stay together after she reveals her desire to separate, she says poignantly: “I guess we could try.”

Indeed, Cunningham is so subtle that only at the novel’s end does it become clear that Mizzy, despite his symbolically loaded name, was not just his parents’ mistake but Peter’s as well.