While chasing drug traffickers, a former agent finds himself stranded in a small mountain town. There, he finds an entrance to a mysterious shadow-filled world. Along with the leader of the mountain guards, they experience a strange adventure in this new territory.

The queen of the human tribe gave birth to twin girls. Respected by the entire tribe, the older sister Qing Kui, who is gentle and kind, is betrothed to the heavenly prince. The younger sister, Ye Tan, smart and cunning, shunned by her own people, is betrothed to the demon prince. Due to a mix-up, the two sisters are married off to the wrong husbands. It paves the way for two beautiful romances and also ignites a conspiracy that shakes the four realms.

Hu Bayi and Fatty Wang had planned to go abroad with Shirley Yang. However, they were entrusted by Professor Chen to travel to the Coral Spiral with Mr. Ming to search for the Qin Emperor's Bone Mirror. They befriended Ruan Hei, Gucai, and Duoling on Coral Temple Island. Together, they set sail. One night, they were sucked into the underwater cave of Guixu. In despair, Hu Bayi and Shirley Yang decided to risk their lives using the Sun-shooting wooden mechanism to lead everyone out of Guixu.

In ancient times, the Human Emperor, Zhao Ming, petitioned on behalf of the people and sacrificed himself to resist the divine realm. After Zhao Ming's fall, his beloved, Hun Dunzhu, risked her life to save a wisp of his soul, setting up the cycle of reincarnation for eternity. In the distant future, Zhao Ming reincarnated as Xie Xuechen, the leader of the Immortal Alliance, while Hun Dunzhu became the Holy Maiden Mu Xuanling in the Dark Domain. The two finally reunited in the mortal realm but had forgotten their past, becoming adversaries in a "righteous versus evil" struggle. Mu Xuanling saved the heavily injured Xie Xuechen in the Dark Domain and coerced him to travel together in gratitude for saving his life.