Selvi, Tamannaah Bhatia, and her family embark on a boat to a temple in Assam during a colorful festival. When the daughter is wounded and her blood spills into the river, the shapeshifting demon Baak is unleashed. Baak slays the girl and then takes her form. A desperate priest traps Baak’s soul inside a vessel, forcing it to inhabit his daughter’s likeness forever, all to spare his wife from losing her family.
The story shifts to a village where Selvi and her husband, Santhosh Prathap, live with their children, Sakthi and Saravanan Jr. Heartbreak strikes when Santhosh dies of a heart attack in the forest, and Selvi is found dead, apparently hanging from a well. Witnessing her mother’s death, Sakthi slips into a coma. Selvi’s brother, Sundar C, an advocate, arrives with his aunt to offer support to the grieving children.
In the same village, Maaya, the zamindar’s granddaughter and a doctor, is assigned to care for Sakthi. Soon, the family begins to experience eerie phenomena within their home. One day, Maaya encounters a spirit by Sakthi’s bedside and tells Saravanan’s aunt, who urges secrecy to protect the family’s interests—hinting at selling the palace and using the proceeds to build a hospital for Maaya.
Saravanan becomes convinced that Selvi’s death was not a suicide. He and Ravi, the village president’s son, go to the police, only to be dismissed by an unhelpful inspector. Ravi later shows Saravanan a video of his late brother-in-law being stalked by a swami. When a jeep ride turns deadly, a spirit attacking in the night leaves Ravi missing and the jeep wrecked, with only the video camera recovered, still recording the swami.
The police eventually back Saravanan, and they locate a lair filled with photographs of recent victims—Selvi, Santhosh, Ravi, and Sakthi. The evidence convinces them to hunt the swami. Saravanan uncovers a chilling pattern: Sakthi, the inspector, and Ravi share the same birthdate and a distinctive red mole, and he warns Maaya to guard the children.
An Assamese priest arrives, claiming to seek his missing daughter and attempting to approach Sakthi, only to be repelled by Selvi’s spirit. In a brutal turn, the inspector dies after being impaled by a vel, and Sakthi awakens from her coma, now protected by Selvi’s ghost. Through interrogation, the swami reveals Baak’s true nature—an evil spirit that can live in water and on land, its power diminished only because its soul was trapped by the priest. Baak has followed the villagers when they moved and eventually recovered its hidden soul. To restore strength, Baak plans to sacrifice Sakthi, the inspector, and Ravi.
Baak kills Selvi’s husband and takes his form to approach Sakthi, but Selvi sacrifices herself to shield her children and returns as a protective spirit. The swami warns Saravanan to safeguard Sakthi at all costs to prevent Baak from becoming immortal.
Baak attacks the police station, injuring people, but the swami manages to drive him away. In a tense moment, Maaya is halted at the gate by Selvi’s spirit while attending Sakthi’s birthday party. Testing reveals that Baak has been impersonating the swami after killing him outside the station. Confronting the president, they uncover the swami’s corpse in the trunk of the president’s car. The president reveals that the swami had gone to the graveyard to destroy Selvi’s spirit and her remains. Saravanan arrives too late, witnessing his sister’s spirit vanish while pleading for Sakthi’s safety.
Baak resurges to claim Sakthi, but Maaya escapes with her toward the temple festival. There, Saravanan battles Baak inside a colossal Asura sculpture, and at the festival’s climax, a divine spirit destroys both the sculpture and Baak.
With the danger ended, Saravanan reassures Maaya that the palace will be converted into a hospital so she can continue serving the village. Outside, Sakthi and Sakthi’s siblings play throwball with their mother’s spirit, a final image that shows she remains watching over them as the credits roll.
