Kalvanin Kadhali is the story of a dacoit and his beloved, Muththaiyan and Kalyani. At the PoonkuLam village, Kalyani falls for good-hearted Muththaiyan. Circumstances brand Muththaiyan a dacoit, but Kalyani remains steadfast in her love. Evading the police, Muthaiyan leads the life of an exile in the forest. When things come to a head, Muththaiyan and Kalyani decide to run away to some far-off place and settle down to marital bliss. Muththaiyan's loyal friend Kamalapathi, who is a stage actor makes all arrangements for their escape. In order to hoodwink the vigilant police inspector Shastri, Kamalapathi disguises himself as a woman and goes to the forest to meet Muthaiyan and appraise him of the plans. When Kalyani comes to the appointed place, she finds Muthaiyan embracing another woman. Not realizing that it is Kamalapathi whom Muththaiyan is expressing his heart-felt thanks to, she suspects her lover's loyalty and runs away in a rage. Inspector Shastri, who is also in disguise, meets Kalyani at this juncture and enquires Muththaiyan's whereabouts. Unthinking in her anger, Kalyani blurts out Muththaiyan's location. Seeing Shastri run with his gun, Kalyani realizes that he is a police officer, and runs after him. The story ends in tragedy where the lovers unite in death.