Dr. Saravanan, a psychiatrist, travels to India for a vacation and ends up reconnecting with his foster brother Senthilnathan (Senthil) and Senthil’s wife Ganga. Senthil’s mother Kasthuri hopes that Senthil will marry Priya, the daughter of his father’s cousin Kandaswamy, in order to reunite the two branches of the family after thirty years of separation sparked by Senthil’s father choosing Kasthuri over Akhilandeshwari, Kandaswamy’s sister. Despite warnings from the village elders, Senthil buys the old Vettaiyapuram mansion and the couple, along with Ganga, move in with Senthil’s family. Akhilandeshwari grows jealous of Saravanan and plots to remove him with the help of her assistant Oomaiyan.
When the family visits a temple, the chief priest reveals the real reason why the Vettaiyapuram mansion is so feared. A hundred and fifty years ago, a king named Vettaiyan traveled to Vijayanagaram in Andhra Pradesh and fell in love with a dancer named Chandramukhi Amruta Khanvilkar Umajirao Junnarkar. She did not return his affection, since she loved another dancer, Gunashekaran. Vettaiyan forced Chandramukhi to return with him, while Gunashekaran stayed nearby. Discovering the affair, Vettaiyan beheaded Gunashekaran on Durgashtami and burned Chandramukhi alive. Ever since, Chandramukhi’s ghost haunts the south-west room of the palace, seeking revenge on the king. The legend also ties into the present, as Priya’s love, Vishwanathan, receives support from Saravanan, who urges Kandaswamy to arrange their marriage.
After hearing the tale, Ganga dismisses it as a story meant to scare thieves away from hidden treasures in the room. Saravanan receives an email about a patient and tells Senthil he’ll call if anything comes up before leaving. Ganga obtains the room key from the gardener’s granddaughter, Durga, and unlocks the door. Soon after, strange occurrences unfold in the house: a ghost frightens the residents, objects break on their own, and Ganga’s sari catches fire. Suspicion falls on Durga as the source of the disturbances, and Senthil summons Saravanan to solve the mystery.
When Saravanan returns, a mysterious being seems to try to kill Priya. Attempts are made on Senthil’s life with poison and by pushing a fish tank, and a mysterious voice sings through the night. Saravanan investigates the escalating phenomena and pieces together what is happening. Ganga vanishes during the wedding reception of Priya and Viswanathan, prompting Saravanan to search for her. He is nearly killed by Oomaiyan, who has been dispatched by Akhilandeshwari. Saravanan subdues Oomaiyan and, with Senthil’s help, discovers Ganga, who is being manipulated under the belief that Viswanathan is her lover Gunashekaran.
Saravanan reveals that Ganga suffers from a split personality and has taken on Chandramukhi’s identity. He explains that Ganga tried to kill Priya and Senthil and to frame Viswanathan, because, in Chandramukhi’s view, Viswanathan is Gunashekaran who resides in the same house. The only way to stop the danger is to make Ganga believe Saravanan is dead, a ruse that mirrors the exorcism strategy: Saravanan pretends to be Vettaiyan and disrupts a puja conducted by the exorcist Ramachandra Acharya by speaking to the ghost to learn its wish.
Akhilandeshwari overhears this plan and, moved by the potential sacrifice, apologizes to Saravanan. In the final confrontation, in the dance hall, the family and Ramachandra Acharya permit Chandramukhi to burn Saravanan alive. Ramachandra Acharya blows smoke and ash on Ganga’s face as she holds a torch to complete the ritual. Senthil then opens a trapdoor to let Saravanan escape, and an effigy of Vettaiyan is burned instead. Believing Vettaiyan to be dead, Chandramukhi leaves Ganga’s body, which cures her. The two families are reunited after thirty years; Saravanan and Durga (the gardener’s granddaughter) fall in love, and Swarna and Murugesan become parents eight years after their marriage.
