In the opening scene, two elderly men discover a dead corpse of Samyuktha, a 15-year old school student, who was brutally murdered. Arun Kumar is an aspiring filmmaker who wants to make a movie on psychopaths. After multiple rejections and pressure from his family, Arun becomes a SI in the T.N.P.D, with the help of his brother-in-law, CI Das, a police officer himself. He moves in with his sister Kokila, Doss and their daughter Ammu. Ammu gets into trouble in school and asks Arun for help, so he meets her teacher Viji at school. He befriends Viji and her hearing and speech impaired niece, Kayal.

Meanwhile, Arun investigates the abduction of a school girl, Amudha. Arun finds similarities between Samyuktha and Amudha's case, due to the mutilations on a doll found at Amudha's house. But his attempts to convince his superior officer, ACP Lakshmi, go futile. A few days later, Amudha's mutilated corpse is found. The pathologist Dr. Nandan, suggests that the perpetrator followed a similar modus operandi like Samyuktha. Over the next few days, another hearing impaired girl named Meera, from Viji's school is abducted and killed. The search leads to Inbaraj, a teacher at the new school Ammu is enrolled. Inbaraj is a pedophile who forces girls into irrumatio. Ammu herself narrowly escapes Inbaraj when Arun nabs him after getting a tip off from another victim Sharmi.

Inbaraj admits to being a sexual predator but denies the murder charges. In a bid to escape, he holds Venkat, a policeman, at gunpoint, but Arun guns Inbaraj down. The same day, Ammu is abducted from her birthday party at home and Arun finds her corpse in their car trunk. To make things worse, Arun is suspended for his negligence on shooting Inbaraj. Dejected and angry, Arun unofficially investigates the case himself with the help of few policemen. Finding an audio clip from Meera's hearing aid, he traces a piano tune back to a lady magician Annabella George, who performed at all the victims' schools. Arun finds that Annabella picks her victims by randomly calling them on to the stage, she then kills them within the next few days and her next target would be a girl named Sanjana. He tries to warn Sanjana.

Despite constant surveillance, she is abducted. Arun and his team track her location and save Sanjana from being murdered. Anabella escapes, but her real identity is revealed to be one Mary Fernandez, who was accused of murder a long time ago. Arun suspects that since her identity is out, Mary might falter in her modus operandi and deviate from her intended targets. He meets Rajamanickam, a retired cop, to collect information. Rajamanickam tells about Mary's son Christopher who has Werner Syndrome (progeria), a hormonal disorder that causes him to appear aged. Christopher performs magic tricks brilliantly and also plays piano well. He is an outcast at school, but a girl named Sophia befriends him.

Christopher develops feelings for Sophia and he proposes to her, but he is heartbroken when she turns him down, since his condition has rendered him impotent and he cannot have a love life. Sophie also started avoiding him after this incident. Their conversation is overheard and Christopher is traumatized after many of the boys in his school humiliate him in the school. Mary learns of this and hacks Sophie to death, where she along with Christopher are arrested and sent to prison. They were believed to be dead in an accident, but Rajamanickam says that perhaps, Mary is still alive and has become a psychopath. Arun reaches Rajamanickam's house only to find him dead. He sees Rajamanickam's evidences but ACP Lakshmi detains him and forbids him from following this case.

Arun discovers that Rajamanickam had pieced information from photographs - revealing that it was Christopher disguised as Mary, who was long dead in an accident. Before Arun can act on this, Christopher attacks Viji and abducts Kayal. While trying to apprehend Christopher, Venkat is killed. Kayal escapes and is found by Dr. Nandan, who tries to hide her in his facility, but Christopher kills Nandan. Arun tracks down Christopher on time, and after a prolonged fight, kills him and saves Kayal. The media finally reports an end to the murders done by Christopher and Arun gets a chance to make a film about a psychopath fulfilling his dream.