Dr. Saravanan, Rajinikanth, a psychiatrist, travels to India on vacation and reconnects with his foster brother Senthilnathan, Prabhu, and Senthil’s wife Ganga, Jyothika. The household is framed by Senthil’s mother Kasthuri, who hopes Senthil will marry Priya, a daughter of Kandaswamy, Nassar, to reunite the two branches of the family after thirty years of estrangement, a rift sparked when Senthil’s father chose Kasthuri over Akhilandeshwari, Kandaswamy’s sister. Despite the village elders’ warnings, Senthil purchases the grand Vettaiyapuram mansion and moves in with his wife and the rest of the family, while Akhilandeshwari, Sheela, grows fiercely jealous and conspires with Oomayan, Sonu Sood, to remove what she sees as an obstacle to her lineage.
During a temple visit, the chief priest reveals the dark reason behind the mansion’s fearsome reputation. A hundred and fifty years earlier, the king Vettaiyan fell in love with a dancer named Chandramukhi, who, however, loved Gunashekaran. When Vettaiyan learned of their bond, he forced Chandramukhi to stay with him and be married, while Gunashekaran remained nearby in a separate house. Jealousy and tragedy followed: Gunashekaran was beheaded by the king, and Chandramukhi was burned alive. Since then, Chandramukhi’s ghost has haunted the south-west room of the palace, seeking revenge on the king. Against this backdrop, Vishwanathan, a dance professor, and Priya’s romance receive Saravanan’s blessing as he asks Kandaswamy to arrange their marriage.
After hearing Chandramukhi’s tale, Ganga, who suspects the story is a fabrication meant to deter intruders from treasure, is eager to test the room’s secrets. Saravanan receives a prompt to attend a patient and promises to call Senthil if anything arises before he leaves. Ganga obtains the key to the room from the gardener’s granddaughter, Durga, Nayanthara, and opens the door. Soon after, the household is beset by strange occurrences: a ghostly presence, objects breaking on their own, and Ganga’s sari catching fire. Suspicion falls on Durga, and Saravanan is summoned to investigate, as a sudden line of danger closes in on Priya.
Ganga vanishes during Priya and Viswanathan’s wedding reception, and Saravanan searches for her, barely escaping an attack by Oomayan, who has been dispatched by Akhilandeshwari. With Senthil’s help, Saravanan subdues Oomayan and uncovers Ganga, who is revealed to be clinically haunted by a split personality and haunted by Chandramukhi’s identity. He explains that Ganga’s condition led her to threaten Priya and Senthil and to misdirect Viswanathan, whom Chandramukhi believes to be her former lover Gunashekaran because he resides in the same house where Gunashekaran once did. The only way to halt this cycle is for Ganga to believe Saravanan is dead, a ruse that requires him to embody Vettaiyan and disrupt a puja conducted by the exorcist Ramachandra Acharya, Avinash, by engaging with the ghost to learn its wishes.
Akhilandeshwari overhears Saravanan’s plan of self-sacrifice and eventually apologizes. In a climactic confrontation in the dance hall, Chandramukhi’s spirit seems to gain control as the family and Ramachandra Acharya permit her to burn Saravanan alive. Ramachandra Acharya then uses smoke and ash on Ganga’s face when she is handed a torch to carry out the burning. Senthil opens a trapdoor, allowing Saravanan to escape, and an effigy of Vettaiyan is burnt in his stead. Convinced that Vettaiyan is dead, Chandramukhi departs Ganga’s body, which restores her to herself. With the haunting subdued, the two families are reunited after thirty years; Saravanan and Durga fall in love, and Swarna, Suvarna Mathew, and Murugesan, Vadivelu, become parents eight years later.
