The arrangement : a novel / Sarah Dunn.

Enhanced descriptions from Syndetics:

A hilarious and emotionally charged national bestseller about a couple who embark on an open marriage -- what could possibly go wrong?

Lucy and Owen, ambitious, thoroughly-therapized New Yorkers, have taken the plunge, trading in their crazy life in a cramped apartment for Beekman, a bucolic Hudson Valley exurb. They've got a two hundred year-old house, an autistic son obsessed with the Titanic, and 17 chickens, at last count.

It's the kind of paradise where stay-at-home moms team up to cook the school's "hot lunch," dads grill grass-fed burgers, and, as Lucy observes, "chopping kale has become a certain kind of American housewife's version of chopping wood." When friends at a wine-soaked dinner party reveal they've made their marriage open, sensible Lucy balks.

There's a part of her, though-the part that worries she's become too comfortable being invisible -- that's intrigued. Why not try a short marital experiment? Six months, clear ground rules, zero questions asked. When an affair with a man in the city begins to seem more enticing than the happily-ever-after she's known for the past nine years, Lucy must decide what truly makes her happy: "real life," or the "experiment?"