After Chen An's father dies suddenly, his young stepmother, Bai Zhiyue, is immediately targeted by the village bachelors who spread rumors and mock her due to strange physical symptoms. Though Chen An harbors forbidden feelings for his stepmother and tries to protect her, his cousin Lin Qing—a feng shui master—returns unexpectedly and declares that Bai Zhiyue is a venomous serpent demon from the southern borderlands seeking revenge. Lin Qing points out Bai’s odd behaviors—her fear of realgar (a traditional Chinese insecticide), wrapping her legs in silk at night, and secretly keeping dead frogs—and claims the sudden red snake-like markings appearing on Chen An’s skin are signs of poisoning by a curse. Through persistent manipulation and a trick involving a "gossip mirror" that supposedly reveals true forms, Lin Qing drives Chen An to the brink of madness, making him doubt whether the woman he loves is truly human. To eliminate Bai Zhiyue completely, Lin Qing colludes with Wang Laizi, a lecherous villager, and Zhao, another bachelor, lying about a giant golden snake lurking in the mountains. In reality, she sets a trap to lure Chen An away under the pretense of catching the snake, allowing the thugs to break into the house, abduct Bai Zhiyue, and ruin her reputation—intending to force the supposed "demon" to reveal itself. Chen An eventually awakens to the truth and rushes back home, only to find the two ruffians either dead or insane in the wild "snake den," with clear tracks of a massive python nearby. Seizing the moment, Lin Qing incites the villagers, falsely accusing Bai Zhiyue of murder, then attacks her with a knife and sets fire to the house, attempting to burn her alive. In a desperate climax, a huge white python suddenly emerges to shield Bai Zhiyue. She commands the beast to retreat from devouring Lin Qing and reveals the truth: she is not a demon but a descendant of the Nanshan Snake Clan, and the giant python named "Dabai" is her spiritual companion and beloved pet. Her frail health, habit of wrapping her legs at night, and feeding dead frogs to the snake stem from ancient customs and severe contagious eczema. What Chen An experienced as a curse was merely a skin infection. Lin Qing’s entire mad scheme stems from her long-standing secret love for Chen An and jealousy over Bai Zhiyue winning his affection. In the end, Lin Qing is arrested and driven to madness. Chen An, filled with remorse, reconciles with Bai Zhiyue, and their family welcomes Dabai—the great protective serpent—as a new member.
