During the Yongle period of the Ming Dynasty, undercurrents surged under the prosperous times.
Xuan Mo, a young man whose life experience is a mystery and whose memory is incomplete, was thrown into prison for being involved in a strange "copper coin case". In a desperate situation, he was protected by a mysterious eunuch who was the supervisor of rituals and was placed in an institution that was not recorded in any official documents - the Huangming Case Library. He was dedicated to assisting the old eunuch Cao Mu (Eunuch Cao) in investigating those unsolved and strange cases that "hurt the peace of heaven and hinder the hearing of the saints".
He has no official position, but he can step into the shadows that are difficult to reach by the Ministry of Justice, Jinyiwei and Dongchang; he has insight into people's hearts and can always pry open iron-clad mysteries from the details of ancient books and local chronicles, medical horoscopes and craftsmen's work. From the deep Forbidden City to the noisy banks of the canal, from the chilling Jiubian Military Town to the misty Jiangnan gardens, one after another incredible cases happened one after another, as if there was an invisible hand, smearing bloody and secret symbols on the glorious scroll of Yongle's prosperous age.
While Xuan Mo is pursuing the truth, he is also pursuing his own past. And every clue vaguely points to the past "Jingnan" event that changed the destiny of the empire, and to an organization shrouded in fog - the "Qianlong Society".
Seven strange cases, like seven keys, are about to open up a period of history that was deliberately buried, and a shocking secret that could overthrow a dynasty.
