In 1843, two sisters from a North Carolina farming family climbed into bed with their husbands, the most famous men in America: the original “Siamese twins,” Chang and Eng Bunker, who were joined at the chest by a band of cartilage. They lived this way for more than three decades. Between them, they had twenty-one children. Christina Baker Kline, who happens to be a distant relative of those sisters, has spent years trying to imagine what such a marriage might have actually felt like. The result is The Foursome by Christina Baker Kline, a novel that resists almost every easy framing the premise invites. What the Novel Is About (Without the Spoilers) Sarah and Adelaide Yates are daughters of a once-prominent Wilkes County family whose social standing has been bruised by an unnamed scandal. When Chang and Eng arrive in town with their wealth, their international fame, and their unmistakable presence, the gossip is immediate. The bold elder sister Addie sees a chance to reclaim her future; the quieter Sallie, who narrates the book, hesitates, …