Francis "Frank" Clemens, a middle-aged financial consultant with a fulfilling job and comfortable marriage on the East Coast, finds himself engaged in an affair. His mistress, Josephine "Billy" Delielle, works as an economist. They meet at an anniversary celebration for a journal to which they both contribute on occasion. Billy, who isn't fond of social engagements, asks if Frank wants to get out of there. Their affair starts platonically, but over the course of a year, their lives become more intertwined as they develop romantic feelings for each other. They talk on the phone every day and see each other when their spouses are at work or out of town. By Frank's standards, Billy is a slob, especially when compared to his own wife Vera. Billy is also much less sociable than Vera, preferring silence to empty conversation and detesting cooking. In addition, while Frank and Vera have been married for many years and have two grown children, Billy and her husband Grey are just starting their lives together. Both Frank and Billy appear to be in happy relationships with their respective spouses—though Billy rarely says much about her marriage—and yet the two are drawn to each other and are very much in love. One week, when both Vera and Grey are away on business trips, Frank rents a cottage in Vermont and invites Billy to join him. She is not thrilled at the idea, but she agrees to go. They spend most of their time in bed and subsisting off of sandwiches. Frank enjoys it, but he realizes that he and Billy are not compatible. They avoid conversations about the state of their relationship until the drive home, where they both agree that their affair is bound to end while simultaneously not wanting it to. Their lives outside of this affair are too stable and not able to accommodate their romance. They return to their lives apart from each other, now more conscious of the fact that every encounter together from here on out could be their last.