The film tells a fictional story, but built upon the human rights violations by the Police and the prison authorities in India during the nationwide emergency of 1975-1977, when the fundamental rights of the citizens were suspended.
The story unfolds as Unnikrishnan (Mammootty), a convict, now free from the jail tells his tragic love story to his fellow passengers in a school bus. An orphan and a forest officer by profession, he falls in love with a local girl, Thulasi, during his stay at a forest area. They decided to get married and he sets off to inform his marriage to his best friend. On his way back the police arrests him as a suspected criminal, who has some visible similarities of Unnikrishnan. There he accidentally kills a police man and gets life imprisonment. During his early days at jail, he writes a letter to Thulasi asking to forget him. When his prison term was about to complete, he wrote a letter to light a lamp if she still waits for him. After long years of torments in the jail he goes to meet Thulasi, and does she still waits for him? That's the question of his fellow passengers too.