Wisit (played by Thanwa Suriyajak), a second-level civil servant at the Ministry of Tourism and Sports, is a passionate collector of antiques. During a work trip to the Ayothaya Floating Market in Ayutthaya, he witnesses a traditional weapon performance that suddenly turns chaotic when a swordsman becomes possessed and attacks the audience. Amid the panic, Praewphan (played by Kemmanij Jamikorn), the daughter of a high-ranking official, is nearly struck. Wisit heroically pulls her to safety and shields her from harm. Just as the spirit is about to strike him, a beautiful celestial being appears and uses her divine power to subdue the vengeful ghost, saving both Wisit and Praewphan. Before Wisit can comprehend what happened, the mysterious woman vanishes.

Back in Bangkok, Wisit is inexplicably drawn to an antique shop where he discovers a serpent-headed ring. Unaware of its hidden power, he purchases it. That night, the same celestial woman appears in his bedroom—Phit (also played by Kemmanij Jamikorn), a spirit bound to the ring. She reveals that she has waited lifetimes to reunite with him, whom she calls “Khun Duer,” and that only he can help her reconnect with her younger sister and free her from a karmic curse.

Meanwhile, Praewphan begins having terrifying dreams of a Thai noblewoman bleeding from the mouth. Wisit, thinking it’s all coincidence, continues wearing the ring. Phit, now able to appear in modern form, follows him everywhere. When Wisit tries to destroy the ring, Phit pleads with him, offering to save his mother, Fueang Khajorn (played by Duangdao Jarujinda), from a looming danger in exchange for keeping the ring. Her prediction comes true, and Wisit agrees.

Praewphan eventually finds Wisit again, and Phit is overjoyed to be near her sister once more. However, due to a vow made in a past life, Phit cannot reveal herself to Praewphan.

In a past life, Wisit was a nobleman loved by twin sisters—Phit, the elder, and Praew, the younger. Wisit loved Phit, which drove Praew into a jealous rage. She poisoned Phit with a deadly flower tea. After Phit’s death, their father forced Wisit to marry Praew, but upon learning the truth, he renounced worldly life and became a monk. Praew, heartbroken and vengeful, vowed to follow him through every lifetime until he loved her. Phit’s spirit, bound to the ring he once gave her, remained in sorrow, watching over her sister.

Now, Phit needs Wisit’s help to break Praewphan’s karmic bond. But things are complicated—Phit cannot reveal the past, and Wisit is entangled with Nongram (played by Kanyarat Pongkampanart), a jealous lover. Fate intervenes when Dr. Banjop (played by Krasek Konin), Nongram’s distant relative, returns from abroad. Nongram falls for him and secretly leaves Wisit. When Wisit finds them together, Nongram confesses and ends their relationship.

Phit seizes the opportunity to bring Wisit and Praewphan closer. However, Dr. Banjop, now obsessed with Praewphan, becomes enraged by her love for Wisit and plots to eliminate him. Phit repeatedly saves Wisit from assassination attempts. A sorcerer uses enchanted wolf tears to allow Praewphan to see Phit with Wisit, shocking her into a heart episode. At the hospital, she is diagnosed with a congenital heart condition—karma from her past life.

Phit, deeply concerned, asks Wisit to pretend to be Praewphan’s boyfriend to ease her suffering. Suspicious, Wisit seeks answers from Luang Pu Thian (played by Sucheow Pongwilai), a revered monk, through his friends Sawang and Phanu. The monk reveals the truth about their past lives.

Bound by heavenly law, Wisit cannot tell Praewphan the truth. Phit, knowing Wisit now understands everything, begs him to marry Praewphan so she can reincarnate. Wisit agrees. Praewphan, overjoyed, breaks off with Banjop. Enraged, Banjop hires a sorcerer to curse Wisit before the wedding.

On the wedding day, Wisit vomits black blood and worms from the curse. Meanwhile, Banjop lures Praewphan to a safe house and tries to assault her. Phit, now a wandering spirit, gathers her last strength to protect her sister. But karma strikes—Banjop throws Praewphan onto the bed, triggering a fatal heart attack. As her soul departs, she sees her past life and realizes her sin. She begs Phit for forgiveness, which Phit grants.

In a twist of fate, Phit’s soul merges with Praewphan’s body. The karmic debt is repaid. Banjop, fleeing the scene, crashes into a truck and dies after seeing the ghost of Nongram and her child.

Luang Pu Thian arrives in time to lift the curse from Wisit. Phit, now in Praewphan’s body, reveals her identity by calling him “Khun Duer.” They marry and live happily, fulfilling the promise made in a past life. Phit passes the serpent ring to Praewphan’s soul as a symbol of their eternal bond—until they meet again in another life.