Based on lots of historical fact about the Grimké sisters originally of Charleston, SC, born into the land and slave-owning class of the plantation south. Both became abolitionists and feminists. While I do suspect it’s possible Monk Kidd overestimates how in favor of racial equality the sisters were (uncommon at the time even [sometimes especially] within abolitionist circles), it seems most of her characterization of them and their lives is rooted in reality. I find it interesting (and… unbelievable) that Monk Kidd has Sarah Grimké actively helping slaves at certain portions of the novel and find the ending unlikely to be historically accurate (white saviorism perhaps), but in all it was a decent read centered in significant research.