Oru Kaidhiyin Diary 1985

David, a prisoner, makes a desperate attempt to escape from prison, but is quickly caught, and his sentence swells dramatically as a consequence. After 22 long years, he is released and goes to visit his dear friend Velappan.

A flashback reveals that Rosy and David were once married and shared a happy life. The couple welcome a newborn son named James, a moment blessed by the party leader, the powerful politician Suryaprakasam, whom David trusts deeply. Suryaprakasam is captivated by Rosy, and he crafts a cruel plan: stage a protest to block the rail traffic, with David as the figurehead, anticipating the arrest that would draw Rosy into his hands for help.

The plan unfolds exactly as hoped. David is arrested, and Rosy comes to him seeking aid. Suryaprakasam manipulates her into handing over her child to his henchman Arumugam, then attempting to disrobe her. Rosy escapes, but the villain is prepared—Arumugam threatens James if she resists. Rosy submits, and Suryaprakasam, with his men, rapes her violently. Struck by shame and humiliation, Rosy hangs herself and leaves a handwritten note detailing the crime. Velappan bails out David, unaware of the depths of the betrayal.

David returns home, proud of his time in jail and his activism, only to be confronted with Rosy’s corpse and her note. He confronts Suryaprakasam at his birthday function, while Inspector Viswanathan and Dr. Unnikrishnan pretend to help but are secretly aligned with the politician. They manipulate Rosy’s note and burn the evidence, all while laughing at the aghast David.

David is framed for Rosy’s murder and is sent to prison, vowing revenge. He leaves his only son, James, in the care of Velappan, who raises him as a hardened enforcer with the aim of aiding David in his vengeance. As time passes, James grows into Shankar, a respected police inspector, creating a painful rift because David cannot trust the life his son leads. This revelation compounds the ache of a man whose life has been torn apart by betrayal.

Seeking solace and a plan, David quietly returns to a church, confessing to the priest that he intends to kill three people, without naming them or himself. The priest warns the authorities, and the hunt for the unknown killer begins to dominate the city. David begins his methodical revenge, tricking his way into Police Headquarters by posing as a priest who knows about the would‑be killer and insisting that he speak only with the Superintendent of Police, S. P. Viswanathan. He identifies himself and forces Viswanathan to call Dr. Unnikrishnan, then sets a Rube Goldbergian trap—a hanging contraption attached to the office door. When Dr. Unnikrishnan arrives and opens the door, Viswanathan slumps from the trap, dying in front of him. David escapes, but a taped conversation reveals the other two victims: Dr. Unnikrishnan and [Suryaprakasam], and the chase intensifies.

David seizes another opportunity, taking Sharadha hostage after she learns of his motive and begins to understand his pain and hunger for justice. With firm protection in place, he eliminates Dr. Unnikrishnan with a telescopic rifle and escapes once again. Sharadha hides David in her basement, a space unseen by the pursuing authorities, keeping him safe for the moment.

Velappan hands over David’s diary to [Shankar], and its pages lay bare the full arc of David’s life up to the moment of his imprisonment. Though outwardly furious at Suryaprakasam, Shankar is urged by DIG RajaManickam to perform his duty and not be swayed by sentiment. The police, meanwhile, scheme to protect Suryaprakasam at the DIG’s residence, while David listens from his hidden refuge. The climactic sequence culminates in David finally killing his last target, [Suryaprakasam], and forcing Shankar to confront the impossible choice of shooting his own father. In a tragic close, David dies alongside Suryaprakasam, and the film ends on a somber note about the cost of vengeance and the toll it takes on the people who try to deliver justice.