Manichitrathazhu

Nakulan and his wife Ganga travel to the Madampalli Tharavad in Kerala for a vacation, ignoring warnings from elder family members. They decide to stay at the apparently haunted mansion, and the rest of the family agrees to join them rather than abandon them. The decision sets the stage for a sequence of eerie events tied to the house.

The family is cautioned to avoid Thekkini, a locked room, as a precaution against malevolent forces. Nakulan and Ganga, however, remain curious and decide to explore its secrets in time. The warning foreshadows the danger to come.

About 150 years ago, Karnavar Sankaran Thambi fell for dancer Nagavalli during a trip to Thanjavur and brought her to the mansion. Nagavalli loved another dancer, Ramanathan, who lived nearby, and the Karnavar killed them when he discovered the affair. Locals say Nagavalli's vengeful spirit remains trapped in Thekkini.

Ganga enlists Alli to unlock Thekkini, hoping to understand the house's mystery. After they succeed, apparitions appear, objects break, and Ganga's sari catches fire, signaling that the room's secrets have awakened. The family grows fearful as the house seems to fight back.

With the haunting intensifying, the family suspects that Nagavalli's spirit may possess Sreedevi, Nakulan's cousin. Puja and other rituals fail to stop the disturbances, deepening the sense of danger in the mansion.

Nakulan summons Dr. Sunny, a renowned Indian psychiatrist based in the United States, to diagnose the phenomena. Sunny's initial investigation reveals a series of eerie events, including attempts on Alli's life and a midnight voice from Thekkini. He begins to piece together a medical explanation behind the haunting.

At midnight, a Tamil song and dance emanates from Thekkini, and a voice impersonating the Karnavar converses with Sunny. The voice identifies itself as Nagavalli and promises revenge on Durgashtami by killing Nakulan. Sunny confronts the spirit and vows to uncover the truth.

To gather more context, Sunny travels to Evoor to speak with locals and uncover legends related to the haunting. The trip broadens his investigation beyond the mansion's walls, helping him connect Nagavalli's history with the present danger.

Sunny uncovers a plot to murder Nakulan by poisoning his tea, and the blame falls on Sreedevi, who is quickly locked in her room. The moment reveals the depth of distrust and the peril facing the family as someone manipulates events from behind the scenes.

On the night before Durgashtami, Ganga reverts to the Nagavalli persona and orchestrates disturbances, perceiving Mahadevan as Ramanathan and Nakulan as Karanavar. Sunny explains to Sreedevi that Ganga is suffering from dissociative identity disorder manifested as Nagavalli. The revelation confirms that the danger is internal to the household.

The family calls in tantric expert Pullattuparam Brahmadathan Namboodiri, who turns out to be an old friend of Sunny and agrees to help cure Ganga. The plan centers on treating Ganga while preventing Nagavalli's vengeance from materializing, with Sreedevi supporting Sunny's approach. This alliance gives the household a fighting chance against the possession.

During Durgashtami night, Ganga slips back into Nagavalli and follows Mahadevan to the ritual preparations, shocking everyone. The Namboodiri confronts Nagavalli and, with Sunny's ruse of swapping Nakulan with a dummy, seemingly defeats her; Nagavalli is temporarily blinded by smoke and ash and becomes dormant.

After the ordeal, Sunny uses therapy to cure Ganga and restore her identity, bringing peace to the household. The family bids farewell to Ganga, Nakulan, and Sunny, and Sunny proposes to Sreedevi, who accepts.