Vijayakanth, Meena, Srividya, Nambiar
Terrorism against India is escalated heavily by Indians trained abroad. Sethupathi IPS (Vijayakanth) is a very efficient cop whose entire family has served the country at some time — his mother Satyabhama (Srividya) is an IAS Officer, his maternal grandfather was a soldier who got a medal for killing 200 enemies (a medal which Sethupathi secretly covets), and his father in law (Vijayakumar) is an Inspector General of Police.
Sethupathi catches terrorist Sivasubramaniam in a hospital and coaxes him to reveal information that their gang is planning a terrorist strike on the Prime minister of India during his meeting with Chief Ministers of various states in Chennai. After divulging this information (owing to the kindness and pity shown by Sethupathi), the terrorist commits suicide with Sethupathi's gun. Using the information Sethupathi is able to save the day and the Prime minister.
Sivasubramaniam's death leads to his brother Sivaprakasham (Raj Mohan) arriving in India. Sivaprakasham is also the leader of this terrorist gang and in addition to the terror strike the gang is planning to launch in India, he also plans to wipe out Sethupathi's family.
Moving opposite to Sethupathi's house, Sivaprakasam pretends to be a very nice man "Satyaprakasham" and manages to fool Sethupathi's mother, wife (Meena), sister, and grandfather and convinces all of them of his true intentions to such an extent that they agree to his engagement with their mute daughter Saraswathi. Sivaprakasam avoids Sethupathi and sees to it that during both the engagement and the wedding Sethupathi is occupied so that he cannot come face to face with Sivaprakasam.
After the wedding the Terrorists take over a school where Sethupathi's wife (Meena) is a teacher and demand for a plane and money to take them abroad. Sivaprakasam brings his wife (Sethupathi's sister) and watches her get gang raped until Sethupathi's wife shoots her, unable to bear her suffering. Sivaprakasam also shoots a boy student of class v.
As the terrorists escape the school towards the plane and take off, Sethupathi has arrived after having killed one of their number, and disguising himself, he elimitates all of them including Sivaprakasam and lands the plane safely (on instructions of the injured pilot).
The movie ends with Sethupathi receiving his coveted grandfather's medal.