The movie starts on a stormy night in Kerala. A large tree branch falls and breaks the roof of an out-house, releasing a dark entity. The woman who inspects the out-house ends up in a hospital suffering from a coma.

In another town her daughter Sanjana (Bipasha Basu) and her husband Kabir (Karan Singh Grover) argue about not being able to spend her birthday together. Sanjana gets a call about her mother's accident and they quickly fly to Kerala. In Kerala, Sanjana begins having paranormal visions that make her believe that her dead conjoined twin's soul is after her. Her husband does not believe her and sends her to his former Professor for spiritual healing.

During the healing sessions she tells the Professor about how her conjoined twin Anjana (Bipasha Basu) always disliked that Kabir liked Sanjana more than her. In fact it was when Kabir told Sanjana that he was coming back home from abroad that Sanjana decided to separate from Anjana. It was during this operation that Anjana died, and Sanjana blames herself for her sister's death. The Professor reassures her that when she sees Anjana in her visions it is the result of her guilt and only a figment of her subconscious.

Back at her mother's place, while getting water at night Sanjana is abducted into the out-house by an unseen entity. Hearing noises Kabir wakes up and finds her unconscious in the out-house. We later learn that Sanjana is now possessed by Anjana's soul.

After this, Sanjana/Anjana can't seem to get enough of Kabir. When the professor meets her again he feels there is something wrong and tells Kabir to keep an eye on her, which she overhears.

The caretaker suggests for them to have a ritual performed after her daughter-in-law sees Sanjana/Anjana messing with the dog. After the ritual Anjana's stronghold escalades and her true colours are shown, resulting in an exorcist being called in.

During the exorcism Anjana reveals that she was actually murdered and urges Kabir to find the truth as she leaves Sanjana's body. After Sanjana wakes up, Kabir threatens to leave her, then Sanjana tells him about years ago when he called her to tell her that he was coming home, Anjana lost her mind and tried to kill her because she too had feelings for Kabir. In self-defence Sanjana hit Anjana on the head with Anjana's glass music box, killing her accidentally. Their mother covered the murder to protect her daughter. After consulting with the Professor they try to find and burn the last remaining thing of Anjana that will set her soul free.

Sanjana, Kabir, the caretaker and her daughter-in-law all go into the out-house following music. There, under the floor they find the dead body of Anjana. The Caretaker and her daughter-in-law go inside to get kerosene to burn the body. The two of them instead end up dead. Then the Professor arrives at the out-house with kerosene, but is actually possessed by Anjana and attacks Sanjana. While Kabir fights him, he finds the locket he gave to Sanjana when they were both young, on what is supposed to be Anjana's dead body. When he confronts Sanjana about it, she finally confesses that she is actually Anjana and she was the one who killed Sanjana with the music box and took her sister's place so she could be with Kabir. Outraged, Kabir decides to leave her despite of her trying to convince him that she loves him, so she hits him on the head with a chair while trying to stop him, but Sanjana's soul stops Anjana while the burning roof falls on Anjana, saving Kabir and the Professor.