At the start of the new year, college student Chu Lan's ordinary life ended abruptly. With his loved ones dead and a demon possessing him, he was drawn into a thousand-year struggle of fate. He became both the "only key" to end the disaster and the "vessel of evil" that could destroy humanity. Forced by destiny, he joined a secret agency to break the endless cycle of the Spirit Calamity. Ultimately, he faced a choice at the end of the battle between good and evil. (Source: Youku)