"Underworld" revolves around a sister and brother - Imali and Suraj who have lost their parents. The two are very attached to each other. Imali a fun-loving girl is carrying on with Mahesh. Mahesh and Suraj join the police and are regarded as officers with grit and honesty. The duo is entrusted with the task of arresting underworld kingpins who are involved in drug trafficking and other nefarious activities which get political backing. They have become a menace to society.