The narrative unfolds with two sisters at a traditional Chinese bath, where they engage in a conversation about immortality. The story soon shifts focus to Blanca, a skilled assassin on a mission to eliminate a Tang general. During this mission, she finds herself caught in a magical brawl, culminating in her submerging into water and consequently losing her memories. Fortunately, she is rescued by Xuan (often referred to as Xu Xian), who brings her to Snake Catcher Village. In this village, the locals are dedicated to catching snakes, as these creatures are esteemed for their supposed connection to immortality.
Initially hesitant and skeptical of Xuan (played by Paul Yen), Blanca (portrayed by Stephanie Sheh) gradually warms up to him. Her journey of revelation begins when they find a jade hairpin that triggers fragments of her memories. Its discovery leads them on an adventure to a special jade workshop, where they hope to uncover more about its magical properties. It’s revealed that the hairpin is also enchanted and has links to Blanca's past.
Meanwhile, tensions run high in the underground realm of the snake-demon people, who exist in oppression under the general. The plot thickens when it is discovered that Blanca's sister, Verta (played by Vivian Lu), is alive and a soldier working for the Snake Master. A snake has intimated that Blanca, who is now partnered with a snake-catcher, is a traitor. Determined, Verta vows to find her sister and return her safely, but with a dire caveat: if she doesn't return with Blanca within three days, the cursed Death Scales embedded within her will explode, claiming her life.
As the story progresses, Xuan and Blanca face challenges including an intense underwater battle with another snake-demon, prompting Blanca to reveal her true demon form. Unfazed by her transformation, Xuan deepens their bond. Their escapades lead them to the special jade workshop, owned by a charming fox-demon who possesses the ability to craft magical weaponry. The workshop owner explains the consequences of wielding the jade wand, which are now surfacing, including memory loss.
After their adventures at the workshop, they return to Snake Catcher Village, where Verta confronts Blanca and makes an attempt to reclaim her sister. This escalates into a physical altercation between the sisters. Amidst the chaos, Xuan and Blanca unwittingly descend into a forgotten underground temple. Here, Blanca’s memories start to resurface, and an emotional moment unfolds when she and Xuan share intimacy in the aftermath of her revelations.
As events unfold, Blanca resolves to return to her demon kind, declaring to Xuan that their different natures—demon and human—create an insurmountable barrier between them. In a twist of fate, Xuan decides to undergo a transformation himself, agreeing to become a low-level demon in hopes of uniting with Blanca. However, this change comes with dire warnings from the fox-demon mistress about his newfound vulnerability as a demon.
Trouble brews as the Dark General sends his second-in-command to capture Blanca, who, overwhelmed and desperate, uses the magic wand again, transforming into a giant python. With the impending clash at Snake Catcher Village, Xuan realizes he must act quickly to protect Blanca from the Dark General's plans, who seeks to exploit her newfound powers. Despite being viewed with suspicion by the villagers for now being a demon himself, Xuan tries to warn them about the impending threat.
As the battle ensues, alliances are tested, and love is put to the ultimate trial; Xuan professes his feelings for Blanca, urging her to escape the conflict with him. However, they soon find themselves ensnared in the Dark General's magical traps. In an unexpected act of sacrifice, Verta manages to distract the General, allowing their allies to engage in combat.
Ultimately, after an intense struggle, the trio—Blanca, Xuan, and Verta—team up to defeat the Dark General. Yet in a shocking twist, the Snake Master harnesses the power of the battle to absorb the spirits of her fallen soldiers, transforming into an immensely powerful demon and turning against Blanca and Verta. It is Xuan’s clever strategy that ultimately leads to the Snake Master's downfall.
Using the last of her strength, Blanca wields the jade wand one final time; she encapsulates Xuan's essence within it, preserving their shared memories and escape with Verta. Fast forward 500 years, and the two sisters, now reminiscing about their tale, decide to venture out to find Xuan's reincarnation.
In a poignant twist of fate, a human at the port crosses paths with the sisters. When Blanca accidentally drops her jade hairpin, he picks it up and introduces himself, causing Blanca to realize he is indeed the reincarnation of Xuan. As the story concludes, a mid-credit scene reveals the fox-demon from the jade workshop arriving at the port, preparing to deliver a mysterious box to a hidden river monster, leaving the audience in suspense for what’s to come.
