In the early 1970s, at the height of the Cultural Revolution, Jan Wong traveled from Canada to become one of only two Westerners permitted to study at Beijing University. One day a fellow student, Yin Luoyi, asked for help getting to the United States. Wong, then a starry-eyed Maoist from Montreal, immediately reported her to the authorities, and shortly thereafter Yin disappeared. Thirty-three years later, hoping to make amends, Wong revisits the...