The story focuses on Television Journalist Pughazhendhi (Arjun) working for "Q TV". During riots triggered by a fight between some college students and bus drivers, which threaten to touch upon the touchy issue of castes, the CM of the state Raghuvaran reveals his unwillingness to take strong action to quell the violence for fear of estranging any of his political bases. To set things right, he then appears on a live interview with Pughazhendi, who had coincidentally captured the CM's earlier unwillingness to take a stand, on camera.
In this interview in response to Pughazh's pointed questioning about the poor working of his government, the CM ducks the question by instead talking about how difficult his job is, and by challenging Pugazh to be the CM for one day. Pugazh reluctantly accepts the seat of the Chief Minister in the place of Aranganathan (Raghuvaran). Educated and vigilant, Pugazh moves fast. He takes care of almost every aspect in a day's time, giving the slum their rightful apartments and getting jobs for the unemployed, suspending inefficient and corrupt government officers. All the way he is assisted by the secretary, Mayakrishnan (Manivannan). As the last act of the day he gets Aranganathan arrested as he is the root of all the corruption. But Aranganathan bails out, passes an ordinance to nullify all orders passed by Pugazh when he was the CM. Taking Pugazh's success as an insult, Aranganathan sends goons to get him killed and destroys his house.The next day, all the remaining parties in the ruling coalition revoke their support to aranganathan and the state Assembly is dissolved for fresh general elections.
Meanwhile Pugazh falls in love with an innocent village girl called Thenmozhi (Manisha Koirala). But her father (Vijaykumar) wants his daughter's suitor to be a government civil worker. So after his tenure as a one-day CM he starts preparing for the Indian Civil Service Examination when his earlier secretary comes in and tells him that Pugazh's popularity has rocketed sky-high and people want him to become the next CM of the state. He refuses but then Aranganathan's henchman attacks the Q TV news agency and wrecks the building in its entirety. Mayakrishnan then tells Pugazh that he has become a part of politics and Aranganathan will never leave him at peace and Pugazh's lawsuit against Aranganathan is bound to fail. But Thenmozhi's father dissuades Pugazh from joining politics. However, on seeing the people's plight and Mayakrishnan's advice he agrees to contest elections.
In the ensuing state elections, his party wins unanimously in all constituencies . But Thenmozhi's father angered by Pugazh's decision refuses to let his daughter marry him. Here, Aranganathan's political allies who deserted him causing his defeat, rejoin him. On becoming the chief minister, Pugazhendhi brings about lots of improvements and quickly becomes an idol in the people's eyes. However his growing popularity is threatened continuously by Aranganathan who uses his henchmen to kill him or at least tarnish is image as a public hero. But Pugazh promptly answers by digging out all accusations against Aranganathan and his allies. This, however, causes a reunion of Aranganathan and his allies. After a failed attempt on Pugazh's life by hiring an assassin, a bomb is detonated at his home killing his parents.
In the final attempt Aranganathan orders his P.A. to destroy law and order and cause bomb explosions in various parts of the city. But a priest is able to overhear a few men planning to detonate bombs. He immediately notifies Pugazh's office via the "Complaint Box" department. Aranganathan's P.A. is arrested and under tactical inquiry by Pugazh and his secretary, he discloses the location of the bombs. A bomb squad successfully defuses all the bombs. Aranganathan, however, uses this success against Pugazh by blaming the young CM for the bomb. Seeing no way out, Pugazh summons Aranganathan to the secretariat and creates a situation such that it would seem as if Aranganathan was there to shoot Pugazh but failed. The security guards shoot down Aranganathan killing him. Pugazh, secretly tells Mayakrishnan the truth but Mayakrishnan believes that Aranganathan deserved it. Thenmozhi's father also comes to realize that Pugazh is in fact a great man who sees duty before everything else and allows Thenmozhi to marry him. The final scene shows Tamil Nadu developing over the years under Pugazhendhi's Government.