One volume of the Commentary on the Water Classic, dedicated to the Northern River system, is missing from all surviving editions, though scholars throughout history have suspected it once existed. The river appears in none of the official histories, yet Li Daoyuan devoted an entire volume to meticulously recording its source, course, tributaries, and the cities along its banks.
The problem is that if this river really exists, it flows through a city that should not exist.
And hidden in that city is a secret powerful enough to shake the very foundations of imperial rule.
