In Nagercoil, 2002, a 17-year-old boy named Bhavani witnesses the murder of his family by his father's rivals. He is forced to take the blame and is imprisoned in a juvenile prison, where he is ruthlessly tortured. As a consequence, he develops a ruthless and audacious personality. Years later, Bhavani escapes from the facility and becomes a criminal in the truck and trade industry. He gradually becomes a terrifying gangster and remains immune to punishment, forcing the prisoners of detention to assume the blame for his crimes. By creating a huge empire for himself, he grows up to the level of his father's former rivals and eventually kills them.

In Chennai, 2019, John Durairaj "J.D." , a university lecturer adored by his students for his friendly approach to students, struggles with alcoholism and fierce resentment on the part of his colleagues. Only Charulatha aka Charu, a newly recruited lecturer at his university, sympathizes with him. After organizing unsuccessful college elections, he is referred to a juvenile correctional facility on a three-month mission that he doesn't remember volunteering for. He reluctantly accepts his new position and is warned by prison authorities about drug abuse and violence raging there, but J.D. pays no attention to it.

Two brothers, Sabari and Manikandan, who are about to surrender for one of Bhavani's murders, tell J.D. a letter he doesn't know, and later that night they try to call him while he's drunk. When they are caught, Bhavani kills them and their bodies are discovered the next day under the ceiling of the investigation room. J.D. is arrested for murders. In grief, Charu reprimands J.D. for his negligent behavior, revealing that it was she who applied him to work, believing that he was the only teacher capable of understanding the needs of prisoners. She is known as an employee of an NGO investigating crimes committed in the facility; the brothers desperately turned to her for help. While in custody, J.D. discovers the brothers' note describing the horrific activities taking place at the facility. Devastated, he hits Bhavani's thugs who were sent to kill him and calls him, promising to pay for the boys' deaths.

After quitting drinking, J.D. slowly takes control of the institution and begins reforming prisoners. His actions are opposed by Das, an older inmate (turned out to be an adult) responsible for controlling younger children. With the help of a young inmate, Undiyal, J.D. discovers crimes in the prison and forces inmates to record their testimony. J.D. discovers that Bhavani regularly makes prisoners take the blame for his crimes. J.D. then records a video of younger inmates, including Undiyal, speaking about Das' crimes at the facility. Bhavani's thugs track down Charu and retrieve the video from her, saving her only because of Undiyal's intervention. Undiyal reveals that selected prisoners are tattooed with the Tamil letter "ப" ("Pa"), which allows them unrestricted access to free food and drugs from Bhavani's associates in exchange for submission for his crimes. J.D. raids appropriate facilities and cuts off the drug supply to the detention facility, much to Bhavani's frustration. He also sneaks into Bhavani's hideout and threatens him and his people with dire consequences, unknowingly holding Bhavani himself by the knife with a pen.

Bhavani retaliates by killing some of J.D.'s colleagues and former students. When J.D. incapacitated by mourning, Das kidnaps most of the prisoners intending to take them from Tamil Nadu with Bhavani's property papers. J.D., with the help of his former colleague and expert archer Vanathi, defeats Das's men and saves the children. J.D. confronts Das and makes him realize that Bhavani will kill him as he is the link between Bhavani and the crimes in custody. Das reforms and transports J.D. to Bhavani meat packing plant with the children. Das overpowers the people sent to kill him, while J.D. confronts Bhavani. Although Bhavani gains the upper hand in the beginning, JD manages to defeat Bhavani. Bhavani calls on J.D. to join him in politics, but J.D. he kills him, thus avenging the deaths of Sabari and Manikandan. When the kids are safe, J.D. and Das surrender to the police.

The detention center is closed by the government and prisoners are put in different state detention centers and prisons, depending on their age. J.D., Das and other adults from the center are sent to prison, where they intend to reform inmates there.