In 19th-century China, seven year old girls Snow Flower and Lily are matched as laotong - or "old sames" - bound together for eternity. Isolated by their families, they furtively communicate by taking turns writing in a secret language, nu shu, between the folds of a white silk fan. In a parallel story in present day Shanghai, the laotong's descendants, Nina and Sophia, struggle to maintain the intimacy of their own childhood friendship in the face of demanding careers, complicated love lives, and a relentlessly evolving Shanghai. Drawing on the lessons of the past, the two modern women must understand the story of their ancestral connection, hidden from them in the folds of the antique white silk fan, or risk losing one another forever.