Hidden deep in the mountains, the recruits at 'Unit 701', China's secret services, operate in a dark, shadowy world. There is the 'wind-listener', a blind surveillance officer who can hear sounds from miles away; the beautiful, unstable maths genius who meets a violent end; the old man who deciphers codes in his dreams; the spy who recounts a dangerous mission from beyond the grave. In this story of conspiracies, geniuses, revolutionaries and terrible moral choices, people sacrifice everything for a world of secrets - until, ultimately, it destroys them.