Unnikrishnan (Mammootty), an ex-convict, 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 arrest him as a suspected criminal, who has some visible similarities to Unnikrishnan. There he accidentally kills a policeman and is sentenced to life imprisonment. During his early days in prison, he writes a letter to Thulasi asking her to forget him. When his prison term was about to complete, he wrote a letter to her to light a lamp if she still waits for him. After long years of torment in the prison he goes to meet Thulasi. Does she still wait for him? That's the question of his fellow passengers too.