After the assassination of a Celestial, Su Mobei, a human, was assigned to investigate the case with a Celestial as his partner. Fearful that the Celestial would suspect him of colluding with the White Way—which could lead to his decapitation, he shared his suspicions with the assassin, Bai Qi, who happened to be his long-lost friend. Follow Su Mobei in uncovering the reason for the assassination, the origin of the Celestials, and the existence of the Moon City.