Gabe and Karen, a happily married middle-aged couple, live in Connecticut. They have been friends with Tom and Beth, another married couple, for many years. In fact, it was Gabe and Karen who introduced their friends in the first place. While having dinner at Gabe and Karen's home, Beth tearfully reveals that she is getting a divorce from Tom, who has been unfaithful.
Tom, who had been away on business, finds out that Beth has told their friends about the looming divorce, and hastens to Gabe and Karen's home. Tom and Beth had planned to tell their friends about their breakup together, but Tom now believes that Beth has unfairly presented herself as the wronged party, and feels he must present his own side of the story.
The time flashes back twelve years, to a vacation home on Martha's Vineyard, when Karen and Gabe introduce Beth to Tom. Over the course of the play, both couples are seen at different ages and stages of their lives. Tom and Beth's breakup affect Gabe and Karen, who first feel compelled to choose sides, and then begin to question the strength of their own seemingly tranquil marriage. They also begin to see the real meaning behind their friendships with Tom and Beth.