Wen Chao of the Qishan Wen Sect tormented and imprisoned the spiritually feeble Wei Wuxian in the Burial Mounds, from which he emerged three months later as a man engaged in demonic cultivation, which was regarded as a dark art. He rejected Lan Wangji's attempts to convince him to stop engaging in demonic cultivation. Wei Wuxian was shunned and lost his reputation because he insisted on engaging in demonic cultivation. Only Lan Wangji stood by him, making every effort to prevent him from succumbing to evil. Wei Wuxian was responsible for his martial sister Jiang Yanli's death as well as the deaths of many other sect's members during the war at Nightless City. Wei Wuxian did this.
Back in the present, Mo Xuanyu revived Wei Wuxian, who was then cursed to remain in his body. Lan Wangji was able to recognise Mo Xuanyu even though he was in his body. Together, they uncovered secrets that eventually enabled them to share historical information.
16 years after his tragic demise, Wei Wuxian, a despised practitioner of dark and demonic techniques, comes back to life. In his second life, he meets up with his soulmate, the revered Lan Wangji, as well as other old friends. Then, Wei Wuxian starts to recall the events leading up to his death, including his early years as a novice cultivator and his ascent into dark magic.
His tragic death's plot, as well as the enigmatic deaths of other people he knew in a previous life, are slowly revealed.