'Diwan' teams up Sharath Kumar and producer P.L. Thenappan. Sarath plays dual role as that of Grandfather Doraisingham and grandson Raghavan. Doraisingham character is based on a true-life person who lived in Thirunelveli years ago. An interesting screenplay and story by Surya Prakash, makes the film gripping till the end.
The story is all about Raghavan, a young man who works in a small restaurant. He falls in love with a girl but the father thinks he is too poor for his status. Humiliated, Raghavan promises himself that he will become rich in a year and marry her. He prevents Aiswarya (Sharmilee) from committing suicide and later learns that she is the daughter of a millionaire and has been deserted by a young man with whom she falls in love. Ragavan decides to restore her to her parents. The car he drives develops a snag and he is attacked by a group of people. Another gang comes to his rescue. They save him because he resembles Duraisingam, whom they worship and who has been sent to prison.
Now comes the flash back, Doraisingham has an ongoing feud with a politician Kandavelu (J.P.R.), ending in Kandavelu going on a bloody massacre at Durai's house. As Durai's sister (Manorama) escapes with his grandson Murugan, the baby is accidentally flung across, a beggar mistakenly picks up Murugan and walks away, leaving his own baby behind. Durai in a vendetta spree kills Kandavelu and his gang and later he surrenders and confesses to his crime. Coming out of the flashback to the present Raghavan alias Murugan visits the prison to see his grandpa but he sees a samadhi of his grandpa built in the cell in the honor of Doraisingham. What follows next is the union of Raghavan and Kiran.
Sarath Kumar has given an excellent performance. Kiran and Sharmilee were average. JPR fails to impress as the villain. Dialogues by Suryaprakash are power packed. S. A. Rajkumar's lyrics and music are average.