When Puyi, the last emperor, was exiled to Manchuria in the early 1930s, it is said that he carried an eight-hundred-year-old silk scroll inscribed with a lost sutra composed by the Buddha. Eventually the scroll would be sold illicitly to an eccentric French linguist named Paul d'Ampère, in a transaction that would land him in prison, where he would devote his life to studying the ineffably beautiful ancient language of the forgotten text.

Our unnamed narrator, a Western student in China in the 1970s, hears this story from the greengrocer Tumchooq-his name the same as that of the language in which the scroll is written-who has recently returned from three years of reeducation. She will come again and again to Tumchooq's shop near the gates of the Forbidden City, drawn by the young man and his stories of an estranged father. But when d'Ampère is killed in prison, Tumchooq disappears, abandoning the narrator, now pregnant with his child. And it is she, going in search of her lost love, who will at last find the missing scroll and discover the truth of the Buddha's lesson that begins “Once on a moonless night...” in this story that carries us across the breadth of China's past, the myth and the reality.