After the death of the Tamil Nadu Chief Minister Ganapathy, the ruling party selects Narayanan, a corrupt politician and ex-rowdy, as their new party leader and Chief Minister. Ponnusamy, a party member who wants to climb to the top, tries to block the move, but Narayanan retaliates by planting a bomb in his car, leaving Ponnusamy dead. Narayanan's right-hand man is Raghavachari, who advises him on every decision, while minister Ramasamy — who resents Ragavachari — vies to become Narayanan's top ally.
Sudesi is a jobless man with a master’s degree in political science who lives with his mother in the city. For the village festival, Sudesi returns to his hometown, and his relative Selvi, who loves him, tries to win his heart. Back in the city, Sudesi’s servant Kamala informs him that her son Ganesh has gone missing, and Ganesh’s body is later found in a drain by the police. The culprit turns out to be a school teacher; at the police station, the police inspector (Mansoor Ali Khan) promises Sudesi that the teacher will be jailed for a long time. However, the inspector later accepts a bribe from the teacher, and Sudesi takes the case to court.
One day, a beggar steals the handbag of Ragavachari’s mistress Shruti on the street, and Sudesi gives chase. Ragavachari then kills Shruti for the theft, while Sudesi brings the handbag to his house. With his henchmen, Ragavachari plants a bomb to destroy all the evidence. The blast kills Sudesi’s mother and leaves him injured, admitted to the hospital. At the hospital, Selvi hands him the handbag they had taken earlier, and he finds a CD hidden inside. Sudesi then absconds. The private detective Thilak is hired by Ragavachari to locate Sudesi and the CD.
Thilak eventually finds Sudesi, who shows him the video contained on the CD. The footage reveals Narayanan killing Ganapathy in the hospital, a crime Ragavachari recorded with a hidden camera to blackmail Narayanan later. Thilak surprisingly decides to support Sudesi. Sudesi and Thilak kidnap Ragavachari, and Sudesi begins to use the CD to press Narayanan into acting for the public good. Narayanan earns widespread praise for his reform efforts, wins the Legislative Assembly election by a landslide, and thanks Sudesi for shaping him into a better leader, continuing to govern under Sudesi’s guidance.
The story unfolds as a tense interplay of political ambition, personal sacrifice, and a rising citizen-driven push for accountability, showing how corruption can be confronted when a determined individual and an unlikely ally challenge the system from within.
