When people complain that American fiction today is stuck in a rut of cliched infidelities and whitebread middle-class despair, they're probably imagining a book like Stewart O'Nan's new novel, "The Odds." Its plot certainly fits the template: Art and Marion Fowler are a middle-aged couple who have hit the skids both financially (they're out of work and nearly bankrupt) and romantically (Art's been caught cheating). They head from Cleveland to Niagara Falls for a pre-divorce last hurrah of sorts, preparing to bet what's left of their dwindling savings at a casino on Valentine's Day.

O'Nan's tone is almost defiantly compassionate: Richard Yates or Jonathan Franzen wouldn't send this pair to the Falls so much as over them, and John Updike would probably smirk at their Midwestern rubeness. Yet this concise tale doesn't pretend to be a work of social realism -- it's subtitled "A Love Story," after all. And O'Nan earns the reader's empathy with an emotional perceptiveness that's rare among contemporary writers. He respects a man who's willing to make "one dashing, reckless gesture" to honor his dying marriage, and successfully encourages us to do the same.

As Art and Marion prepare for their big bet, their unsteadiness often manifests itself in broad set pieces: When they labor to recapture their lost youth by boozing it up at a Heart concert, they seem as washed up as the band. But the book's engine is its more intimate observations of how the familiar habits of three decades of marriage have broken down, turned strange and uncertain. In the resort elevator, Art recalls that he'd normally steal a kiss from her, but "now, to show support, he held her hand." In the bedroom, Marion slips on a nightie and anxiously asks herself, "Wasn't her nightgown proof of her good intentions?" The temperature has cooled only a degree. They're only inches farther apart. But those small shifts matter.

In 2007, O'Nan published "Last Night at the Lobster," a slim Christmas fable about a dying restaurant. "The Odds" is kind of a cousin to that book, a slim Valentine's Day fable about a dying marriage. Practically by necessity, the new novel is made of sweeter stuff, and some mawkishness creeps into the story. The roulette-wheel, Hollywood-esque plot overworks the love-is-a-risk theme, and the Fowlers' decision to stake their nest egg in a casino isn't entirely convincing.

But that doesn't make "The Odds" an entirely lightweight confection. When O'Nan moves away from the gaudy neon tourist traps and into the heads of its frustrated couple, he captures the emotional machinery that binds and separates two people in love. Call them Midwestern rubes, but they have plenty to say that's worth hearing.

Mark Athitakis is a reviewer based in Washington, D.C. He blogs at americanfiction.wordpress.com.