Plot

After running away from his home, Kumar falls in with a gang and slowly rises through the ranks of the criminal underworld.

A slum dweller, Kokki Kumar (Dhanush) returns from a movie to find his mother murdered by his own father. As his father deranged advances towards him he runs away and starts begging on the streets until he is arrested on false charges. Prison exposes him to a whole new culture and a set of people who train him in a life of crime and violence, until Kumar becomes a consummate gangster. Delving further into the dark world, he murders many to become a powerful mob kingpin and joins hands with crooked politicians in his thirst for more power. As he continues to earn enemies everywhere, Kumar's life is threatened from all directions. Can he survive the wrath of his enemies?—Santhosh

The story is narrated by the main character, "Kokki" Kumar, in a jail cell.

Kumar is a secondary school student who lives in the slums of Pudhupettai, in Chennai. After coming home from a film, he sees his mother's dead body. She was killed by his father, following an argument. After overhearing a conversation between his father and his friend that they plan on killing him too, as he was a witness, Kumar flees from home.

Homeless and with no food, he resorts to begging. He is arrested, under false charges, while he watches the police arrest criminals on the street. After being released on bail, he befriends Mani and the others, all of whom work for a thug named Anbu. Anbu works for the opposition party's leader Thamizhselvan, who is a criminal and local politician. They take Kumar under their wing and give him petty jobs. During a confrontation with rival gangsters headed by the ruling party's politician Murthy, Kumar kills Murthy's brother single-handedly amidst 100 goons, earning the respect of his gang. Anbu makes him join a gang consisting of professional killers. There, Kumar learns the way of being a killer while surviving attacks from Murthy's men. The gang refuses to help Kumar avoid Murthy's men since their intervention would spark a gang war. Kumar murders several of his opponents singlehandedly, earning him respect from the others.

Krishnaveni is a prostitute who works under Anbu. Kumar likes her and asks Anbu to release her. Anbu is shocked at Kumar's audacity and refuses his request. He thrashes Krishnaveni and orders his men to kill Kumar. Kumar approaches Anbu and begs pardon, but when Anbu refuses, Kumar kills him. Thamizhselvan allows Kumar to take over Anbu's business only if he can survive the night from Anbu's men. Kumar survives, and Thamizhselvan makes good on his word.

Anbu's goons refuse to obey Kumar since he is young and inexperienced. But Kumar kills his opposition, as well as his father, and becomes a dreaded don in North Chennai. Murthy is paralysed by Kumar's men for refusing a truce. Kumar then meets Selvi, Mani's sister, and marries her forcibly on the eve of her wedding. Mani tries to kill Kumar unsuccessfully then joins Murthy's gang. Meanwhile, Krishnaveni reveals that she is pregnant with Kumar's child, and Kumar marries her as well.

Mani becomes an informant and testifies in court over Kumar's killings; Kumar threatens Selvi and her mother, and thus avoids charges through witness intimidation. Kumar is the given a post in the party by Thamizhselvan to prevent him from defecting. Due to his increasing crime record and fear of being killed, Kumar asks for a seat as a Member of the Legislative Assembly (MLA) but is ridiculed by everyone, including Thamizhselvan, and ultimately removed after threatening to kill the other members with an aruval. Murthy learns about this and plans to assassinate Kumar and his family.

Fearing for their safety, Kumar sends Krishnaveni and his newborn son away, but Murthy's men intercept them, kill her, and take the baby. He requests Selvi to ask her brother Mani for help, but she refuses and reveals her displeasure at how Kumar ruined her life and that she plans to return to her former fiancé. Mani is compassionate enough to return the baby safely to Kumar. Kumar then gives the baby to a kind-hearted woman, without revealing himself as the father of the child. The kind hearted woman is a married woman with two children, who earns her living by working as a housemaid in four houses. Kumar decides to exact revenge and kills Murthy's henchmen in his residence, but his right hand is crippled during a fight. Murthy ultimately commits suicide, which is then followed by Kumar's arrest.

In the present day, the police and prison warden come to retrieve Kumar from his cell, with Kumar under the impression that he is to be executed. However, during the epilogue, it is revealed that the incumbent Chief Minister arranged Kumar's release and named him as an MLA candidate in the following election. Kumar praises Murthy and ironically states that he would have killed the people responsible for Murthy's death had India not been the birthplace of Gandhi.

In the epilogue, it is also revealed that Kumar served three times as an MLA and twice as the Finance Minister of Tamil Nadu. Despite his political growth, he still could not find his son. Selvi is also revealed to have conducted her second marriage with her former fiance. Two months after her marriage her husband went missing. After that Selvi has been committed to an asylum.