At around 2:00 AM, water overflows from an apartment in Block E, catching the attention of the building’s watchman. When he investigates, he discovers Ramya Sindhu Menon dead in the bathtub from asphyxiation. The case lands with Assistant Commissioner of Police Vasudevan Aadhi Pinisetty, an honest officer who is Ramya’s former boyfriend. Although the scene initially suggests suicide, Vasu doubts the verdict and restarts the investigation to uncover what really happened.
Delving into Ramya’s life, the probe reveals an extramarital affair and several visits to her flat, confirmed by neighbors. Yet Vasu remains unconvinced and suspects a mastermind he dubs Mr. X Krishna. He also revisits his college romance with Ramya, recalling how her father Shriraman refused to give his blessing to their marriage; when Vasu urged Ramya to elope, she declined, and they parted. Ramya later married Balakrishnan [Nandha], a wealthy businessman.
Strange mishaps begin to plague the same apartment: Kalyani [Lakshmi Ramakrishnan] dies by electric shock in the flat opposite Ramya’s; Thiyagarajan, an army veteran, dies when an umbrella tip pierces his neck; and the building’s watchman dies under mysterious circumstances. Vasu connects these deaths to Ramya but can’t yet see the pattern. He assigns a few assistants to live in different flats to monitor any suspicious activity; they report a young man visiting his girlfriend Deepa, and Vasu identifies him as Mr. X and follows him to a theater. Before he can intervene, Mr. X bangs his head on a restroom mirror and seems intent on self-harm. An unseen spirit stops him from saving the man, and Vasu witnesses human footprints walking on water, confirming a supernatural force at work.
Red and water keep appearing as signals of an impending murder. The investigation shifts to a supernatural explanation of life after death, with Vasu learning that a spirit can contact the living through various mediums — including water. He concludes that Ramya’s soul is enacting the vengeance behind the deaths: Kalyani, Thiyagarajan, the watchman, Mr. X, and the troubled Deepa. He informs Balakrishnan that the truth will soon come to light, a warning that unsettles the husband.
Ramya’s backstory comes into focus when Divya [Saranya Mohan], Ramya’s sister, visits Vasu to console him. Ramya’s spirit possesses Divya and recounts the couple’s ups and downs post-breakup. Ramya lived with Balakrishnan for a time, but he disliked anything tied to her past and harassed her. Ramya had warned Thiyagarajan about sexual harassment from another man, and a series of lies is used against her by neighbors and by Thiyagarajan’s return to ruin her reputation. The truth points to Balakrishnan as Ramya’s killer, who drowned her to make the death look like suicide.
Vasu vows to expose Balakrishnan’s crime and bring Ramya’s killer to justice. The confession seems to come when Balakrishnan is confronted, and Vasu uses the opportunity to arrest him. In reality, Ramya’s spirit had possessed Balakrishnan and forced him to confess. The next day, as Balakrishnan is escorted to court, the sky darkens and it begins to rain. Petrol leaks from the police jeep, and a red umbrella dripping with water appears as a final omen as the jeep crashes, implying Balakrishnan’s death and sealing Ramya’s vengeance.
